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The people configuring WAF rules at CDNs tend to do a poor job understanding sites and services that discuss technical content. It's not just Cloudflare, Akamai has the same problem.

If your site discusses databases then turning on the default SQL injection attack prevention rules will break your site. And there is another ruleset for file inclusion where things like /etc/hosts and /etc/passwd get blocked.

I disagree with other posts here, it is partially a balance between security and usability. You never know what service was implemented with possible security exploits and being able to throw every WAF rule on top of your service does keep it more secure. Its just that those same rulesets are super annoying when you have a securely implemented service which needs to discuss technical concepts.

Fine tuning the rules is time consuming. You often have to just completely turn off the ruleset because when you try to keep the ruleset on and allow the use-case there are a ton of changes you need to get implemented (if its even possible). Page won't load because /etc/hosts was in a query param? Okay, now that you've fixed that, all the XHR included resources won't load because /etc/hosts is included in the referrer. Now that that's fixed things still won't work because some random JS analytics lib put the URL visited in a cookie, etc, etc... There is a temptation to just turn the rules off.

> I disagree with other posts here, it is partially a balance between security and usability.

And economics. Many people here are blaming incompetent security teams and app developers, but a lot of seemingly dumb security policies are due to insurers. If an insurer says "we're going to jack up premiums by 20% unless you force employees to change their password once every 90 days", you can argue till you're blue in the face that it's bad practice, NIST changed its policy to recommend not regularly rotating passwords over a decade ago, etc., and be totally correct... but they're still going to jack up premiums if you don't do it. So you dejectedly sigh, implement a password expiration policy, and listen to grumbling employees who call you incompetent.

It's been a while since I've been through a process like this, but given how infamous log4shell became, it wouldn't surprise me if insurers are now also making it mandatory that common "hacking strings" like /etc/hosts, /etc/passwd, jndi:, and friends must be rejected by servers.

Not just economics, audit processes also really encourage adopting large rulesets wholesale.

We're SOC2 + HIPAA compliant, which either means convincing the auditor that our in-house security rules cover 100% of the cases they care about... or we buy an off-the-shelf WAF that has already completed the compliance process, and call it a day. The CTO is going to pick the second option every time.

Yeah. SOC2 reminds me that I didn't mention sales as well, another security-as-economics feature. I've seen a lot of enterprise RFPs that mandate certain security protocols, some of which are perfectly sensible and others... not so much. Usually this is less problematic than insurance because the buyer is more flexible, but sometimes they (specifically, the buyer's company's security team, who has no interest besides covering their own ass) refuse to budge.

If your startup is on the verge of getting a 6 figure MRR deal with a company, but the company's security team mandates you put in a WAF to "protect their data"... guess you're putting in a WAF, like it or not.

>guess you're putting in a WAF, like it or not.

Install the WAF crap, and then feed every request through rot13(). Everyone is happy!

Up until you need to exercise the insurance policy and the court room "experts" come down on you like a ton of bricks.

now you've banned several different arbitrary strings!

Good luck debugging why the string "/rgp/cnffjq" causes your request to be rejected :)

OS-level monitoring / auditing software also never ceases to amaze me (for how awful it is). Multiple times, at multiple companies, I have seen incidents that were caused because Security installed / enabled something (AWS GuardDuty, Auditbeat, CrowdStrike…) that tanked performance. My current place has the latter two on our ProxySQL EC2 nodes. Auditbeat is consuming two logical cores on its own. I haven’t been able to yet quantify the impact of CrowdStrike, but from a recent perf report, it seemed like it was using eBPF to hook into every TCP connection, which is quite a lot for a DB connection poolers.

I understand the need for security tooling, but I don’t think companies often consider the huge performance impact these tools add.

I wish IT teams would say "sorry about the password requirement, it's required by our insurance policy". I'd feel a lot less angry about stupid password expiration rules if they told me that.

Sometime in the past few years I saw a new wrinkle: password must be changed every 90 days unless it is above a minimum length (12 or so as best I recall) in which case you only need to change it yearly. Since the industry has realized length trumps dumb "complexity" checks, it's a welcome change to see that encoded into policy.

I think I like this idea that the rotation interval could be made proportional to length, for example doubling the interval with each additional character. Security standards already now acknowledge that forced yearly rotation is a net decrease in security, so this would incentivize users to pick the longest password for which they would tolerate the rotation interval. Is yearly rotation too annoying for you? For merely the effort of going from 12 -> 14 characters, you could make it 4 years instead, or 8 years, 16, and so on.

Can confirm when I found out I'd be required to regularly change my password the security of it went down significantly. At my current job when I was a new employee I generated a secure random password and spent a week memorizing it. 6 months later when I found out I was required to change it, I reverted to a variation of the password I used to use for everything years ago with some extra characters at the end that I'll be rotating with each forced change...

I do the same but write the number at the end of the password on the laptop in sharpie. I work from home so I've been thinking about making a usb stick that simulates a keyboard with a button to enter the password.

Dangerous. You might accidentally press the button in a group chat.

They would then have an excuse to get one of those mission control button covers.

Why not make use of a password manager?

You can’t open the password manager until your computer is unlocked.

You can put the password manager on your phone or another device.

and now you’re violating a different policy.

I'm not pulling my phone out every time I have to unlock my computer at work. If IT wants my work account to be secure they should change their policies.

As discussed here, the policy is from outside the org.

Unfortunately, lots of end users refuse to read the password policy and won't understand why their password reset interval is "random" or shorter than their colleague's.

> Sometime in the past few years I saw a new wrinkle: password must be changed every 90 days unless it is above a minimum length (12 or so as best I recall) in which case you only need to change it yearly. Since the industry has realized length trumps dumb "complexity" checks, it's a welcome change to see that encoded into policy.

This is such a bizarre hybrid policy, especially since forced password rotations at fixed intervals are already not recommended for end-user passwords as a security practice.

I think the issue is that some people don't actually understand what's going on, so in an attempt at goodwill, they try to "compromise", and "split the difference" if you will. Hell, some people will consider the windows hello pin as a password and force a regular rotation. Combined with policies coming from outside (think insurance and other compliance stuff) which try to cover as much ground as possible, you end up with half-assed implementations like these.

One discourse I hear is that "people will just use the same password everywhere". To which I'll answer, "but we have mfa". "yeah, but the insurance guys".

Not exactly that, but I've had the security team say "sorry about the password policy, we agree it is stupid and counterproductive, but it's required for compliance with X, and we need X to sell to some big customers."

> but a lot of seemingly dumb security policies are due to insurers.

I keep hearing that often on HN, however I've personally never seen seen such demands from insurers. I would greatly appreciate if one share such insurance policy. Insurance policies are not trade secrets and OK to be public. I can google plenty of commercial cars insurance policies for example.

I found an example!

https://retail.direct.zurich.ch/resources/definition/product...

Questionnaire Zurich Cyber Insurance

Question 4.2: "Do you have a technically enforced password policy that ensures use of strong passwords and that passwords are changed at least quarterly?"

Since this is an insurance questionnaire, presumably your answers to that question affect the rates you get charged?

(Found that with the help of o4-mini https://chatgpt.com/share/680bc054-77d8-8006-88a1-a6928ab99a...)

We've been asked that question before on security questionnaires, and our answer has always been, "Forcing users to change passwords regularly is widely regarded as a very bad security practice, and we don't engage in bad security practices." We've never had anyone complain.

I've never had a complaint about anything I put in to a form requesting a quote for insurance. I just get the quote back. Did you write that in the comment expecting an insurance salesperson to call you up and argue passwords with you? Call their back office and say "hey this guy says our password question is crap, get our best guys on it!"?

I just cant imagine any outcome other than it was translated to just a "no" and increased your premium over what it would have otherwise been.

I've also filled out insurance quote forms several times to see the interplay of the questions and price. Quite often many of the questions do not change the quote. So the existence of the question in a form does not imply a change in price, or any true guess at the magnitude of the change at all.

Directly following is question 4.3: "Are users always prevented from installing programs on end-user devices?"

Totally bonkers stuff.

A trend for corporate workstations is moving closer to a phone with a locked-down app store, with all programs from a company software repo.

Eliminating everything but a business's industry specific apps, MS Office, and some well-known productivity tools slashes support calls (no customization!) and frustrates cyberattacks to some degree when you can't deploy custom executables.

That's why this it's been a requirement for Australian government agencies for about 15 years.

In around 2011, the Defence Signals Directorate (now the Australian Signals Directorate) went through and did an analysis of all of the intrusions they had assisted with over the previous few years. It turned out that app whitelisting, patching OS vulns, patching client applications (Office, Adobe Reader, browsers), and some basis permission management would have prevented something like 90% of them.

The "Top 4" was later expanded to the Essential Eight which includes additional elements such as backups, MFA, disabling Office macros and using hardened application configs.

https://www.cyber.gov.au/resources-business-and-government/e...

Then the users start using cloud webapps to do everything. I can't install a PDF-to-excel converter, so I'll use this online service to do it.

At first glance that might seem a poor move for corporate information security. But crucially, the security of cloud webapps is not the windows sysadmins' problem - buck successfully passed.

I don’t think locking down slashes support calls because you will now receive support requests anytime someone wants to install something and actually have a good business reason to do so.

Consider the ones you don't get: ones where PCs have to be wiped from customization gone wrong, politics and productivity police calls - "Why is Bob gaming?", "Why is Alice on Discord?".

It's about the transition from artisanal hand-configuration to mass-produced fleet standards, and diverting exceptional behavior and customizations somewhere else.

If you don’t want exceptional behavior, that’s exactly what you’ll get. In more than one way.

Alice is on Discord because half of the products the company uses now give more or less direct access to their devs through Discord

Coupled with protection against executing unknown executables this also actually helps with security. It's not like (most) users know which exe is potentially a trojan.

This is standard practice for years in big corporations.

You install software via ticket requests to IT, and devs might have admin rights, but not root, and only temporary.

This is nothing new though, back in the timesharing days, where we would connect to the development server, we only got as much rights as required for the ongoing development workflows.

Hence why PCs felt so liberating.

It's a standard practice. And at $CURENT_JOB it's driven by semi-literate security folks, definitely not insurance.

Insurance and liability concerns drive the security folks.

Just wait when more countries keep adopting cybersecurity laws for companies liabilities when software doesn't behave, like in any other engineering industry.

Hello, the security folks in those companies made those up. "cyber insurance" is hogwash. That entire branch has been taken over by useless middle manager types who know to type up checklists in Word but have no understanding of anything.

Are you arguing non technical people should have root access to company owned and managed PCs? Because I can tell you from experience, that will result in a very bad time at some point. Even if it is just for the single end user and not the wider org.

As someone that happens to also be one of those clueless people when assuming DevOps roles in consulting projects, it is a very bad day when some clever user is responsible for a security breach.

A breach can turn out into enough money being lost, in credibility, canceled orders, or lawsuits, big enough to close shop, or having to fire those that thought security rules were dumb.

Also anyone with security officer title, in many countries has legal responsibilities when something goes wrong, so when they sign off software deliverables that go wrong, is their signature on the approval.

Password policy is something rather common, and 'standard' firewalls. Question is in the context of of WAF as in the article. WAF requirement is something more invasive to say the least.

The fun part is that they don't demand anything, they just send you a worksheet that you fill out and presumably it impacts your rates. You just assume that whatever they ask about is what they want. Some of what they suggest is reasonable, like having backups that aren't stored on storage directly coupled to your main environment.

The worst part about cyber insurance, though, is that as soon as you declare an incident, your computers and cloud accounts now belong to the insurance company until they have their chosen people rummage through everything. Your restoration process is now going to run on their schedule. In other words, the reason the recovery from a crypto-locker attack takes three weeks is because of cyber insurance. And to be fair, they should only have to pay out once for a single incident, so their designated experts get to be careful and meticulous.

This is such an important comment.

Fear of a prospective expectation, compliance, requirement, etc., even when that requirement does not actually exist is so prevalent in the personality types of software developers.

It cuts both ways. I've struggled to get things like backups or multifactor authentication approved without being able to point to some force like regulation or insurance providers that can dislodge executives' inertia.

My mental model at this point says that if there's a cost to some important improvement, the politics and incentives today are such that a typical executive will only do the bare minimum required by law or some equivalent force, and not a dollar more.

You can buy insurance for just about anything, not just cars. Companies frequently buy insurance against various low-probability incidents such as loss of use, fraud, lawsuit, etc.

Having worked with PCI-DSS, some rules seem to only exist to appease insurance. When criticising decisions, you are told that passing audits to be able to claim insurance is the whole game, even when you can demonstrate how you can bypass certain rules in reality. High-level security has more to do with politics (my definition) than purely technical ability. I wouldn't go as far as to call it security theatre, there's too much good stuff there that many don't think about without having a handy list, but the game is certainly a lot bigger than just technical skills and hacker vs anti-hacker.

I still have a nervous tick from having a screen lock timeout "smaller than or equal to 30 seconds".

There should be some limits and some consequences to the insurer as well. I don't think the insurer is god and should be able to request anything no matter if it makes sense or not and have people and companies comply.

If anything, I think this attitude is part of the problem. Management, IT security, insurers, governing bodies, they all just impose rules with (sometimes, too often) zero regard for consequences to anyone else. If no pushback mechanism exists against insurer requirements, something is broken.

> There should be some limits and some consequences to the insurer as well. I don't think the insurer is god and should be able to request anything no matter if it makes sense or not and have people and companies comply.

If the insurer requested something unreasonable, you'd go to a different insurer. It's a competitive market after all. But most of the complaints about incompetent security practices boil down to minor nuisances in the grand scheme of things. Forced password changes once every 90 days is dumb and slightly annoying but doesn't significantly impact business operations. Having to run some "enterprise security tool" and go through every false positive result (of which there will be many) and provide an explanation as to why it's a false positive is incredibly annoying and doesn't help your security, but it's also something you could have a $50k/year security intern do. Turning on a WAF that happens to reject the 0.0001% of Substack articles which talk about /etc/hosts isn't going to materially change Substack's revenue this year.

The issue is that the Finance dept will show up and ask why you chose the more expensive insurance. Sure, if you're able to show how much the annoyances of the cheaper company would cost you, they'd probably shut it. But I'd argue it's not that easy. Plus, all these annoyances aren't borne by the security team, so they don't care that much in the end.

My first thought might be to put together a report showing the cost that the cheaper insurance would impose upon the organization which the more expensive up-front option is saving you. Perhaps even serve that up as a cost-savings the finance department is free to then take credit for, I'unno. :P

> Forced password changes once every 90 days is dumb and slightly annoying but doesn't significantly impact business operations.

It negatively impacts security, because users then pick simpler passwords that are easier to rotate through some simple transformation. Which is why it's considered not just useless, but an anti-pattern.

https://250bpm.substack.com/p/accountability-sinks

This is why everyone should have a union, including highly paid professionals. Imagine what it would be like. "No, fuck you, we're going on strike until you stop inconveniencing us to death with your braindead security theater. No more code until you give us admin on our own machines, stop wasting our time with useless Checkmarx scans, and bring the firewall down about ten notches."

> If an insurer says "we're going to jack up premiums by 20% unless you force employees to change their password once every 90 days", you can argue till you're blue in the face that it's bad practice, NIST changed its policy to recommend not regularly rotating passwords over a decade ago, etc., and be totally correct... but they're still going to jack up premiums if you don't do it.

I would argue that password policies are very context dependent. As much as I detest changing my password every 90 days, I've worked in places where the culture encouraged password sharing. That sharing creates a whole slew of problems. On top of that, removing the requirement to change passwords every 90 days would encourage very few people to select secure passwords, mostly because they prefer convenience and do not understand the risks.

If you are dealing with an externally facing service where people are willing to choose secure passwords and unwilling to share them, I would agree that regularly changing passwords creates more problems than it solves.

> removing the requirement to change passwords every 90 days would encourage very few people to select secure passwords

When you don’t require them to change it, you can just assign them a random 16 character string and tell them it’s their job to memorize it.

There's no way I will ever remember it. I will write it down. Let me choose my own password (passphrase if I need to remember it)

> jack up premiums by 20% unless you force employees to change their password once every 90 days"

Always made me judge my company's security teams as to why they enable this stupidity. Thankfully they got rid of this gradually, nearly 2 years ago now (90 days to 365 days to never). New passwords were just one key l/r/u/d on the keyboard.

Now I'm thinking maybe this is why the app for a govt savings scheme in my country won't allow password autofill at all. Imagine expecting a new password every 90 days and not allowing auto fill - that just makes passwords worse.

I'm no expert, but I did take a CISSP course a while ago. One thing I actually remember ;P, is that it recommended long passwords in in lieu of the number, special character, upper, lower ... I don't remember the exact wording of course and maybe it did recommend some of that, but it talked about having a sentence rather than all that mess in 6-8 characters, but many sites still want the short mess that I never will actually remember

While the password recommendation stuff is changing (the US government updating it guidelines last year), it’s generally best practice to not share passwords which itself implies using a password manager anyway which makes the whole “long passphrase” vs “complex” password moot - just generate 32 lowercase random characters to make it easier to type or use the autogenerated password your password manager recommends.

The long passphrase is more for the key that unlocks your password manager rather than the random passwords you use day to day.

There's also login passwords, and depending on how many systems you have to log into, these can be quite numerous. There are some attempts to address this with smartcards and FIDO tokens and so on, but it's not nearly universal yet. At least SSH keys are common for remote login nowadays, but you still need to log into some computer directly first.

I find it rare to have a huge number of machines to log into that aren't hooked up to a centralized login server. Still, nothing prevents you from having passwords for each individual machine that needs it. It's cumbersome to type it in but it works, which is why I recommended all lowercase (faster to type on a mobile device).

Yeah, I've thought about a yubi key or something, but haven't pulled the trigger.

I guess I'm weird, I use my browser, yet I haven't wanted to store that in the cloud, so it doesn't sync to my phone. Let me know if that's paranoia isn't justified. For me, if it becomes more universal, something like a yubi key that I can keep on my key-chain might work.

entropy is stronger than complexity. https://xkcd.com/936/

I wonder how many people have used Correct Horse Battery Staple as a password thanks to this comic

Ah, just mix them up randomly: Staple Battery Correct Horse!

> Makes password "xkcd.com/936"

I believe that these kind of decisions are mostly downstream of security audits/consultants with varying level of up to date slideshows.

I believe that this is overall a reasonable approach for companies that are bigger than "the CEO knows everyone and trusted executives are also senior IT/Devs/tech experts" and smaller than "we can spin an internal security audit using in-house resources"

Why wouldn't the IT people just tell the grumbling employees that exact explanation?

IT doesn't always hear the grumbles, hidden away as they frequently are behind a ticketing system; the help desk technicians who do hear the grumbles aren't always informed of the "why" behind certain policies, and don't have the time or inclination to go look them up if they're even documented; and it's a very unsatisfying answer even if one receives a detailed explanation.

Information loss is an inherent property of large organizations.

> Information loss is an inherent property of large organizations.

That's such an interesting axiom, I'm curious if you would want to say more about it? It feels right intuitively - complexity doesn't travel easily across contexts and reaching a common understanding is harder the more people you're talking to.

On a more micro level, I find it very hard to write good documentation. I always forget something that once pointed out seems obvious. Or worse, the reader is missing some important context that many other readers are already privy to. Not to mention, some people don't even seek out docs before acting.

I imagine this gets amplified in a large org. The docs are lacking, people might not read them anyway, and you get an explosion of people who don't understand very much but still have a job to do.

In small orgs that might happen, in large orgs it's some game of telephone where the insurance requirements are forwarded to the security team which makes the policies which are enforced by several layers of compliance which come down on the local IT department.

The underlying purpose of the rules and agency to apply the spirt rather than the letter gets lost early in the chain and trying to unwind it can be tedious.

If you've read this thread, it would appear that most people here on HN aren't actually involved with policy compliance work dictated from above. Have you ever seen a Show HN dealing with boring business decisions? No. We do, however, get https://daale.club/

I think the problem is any time we are involved with policy compliance work it’s because we get a list with inane requirements on, and nobody to challenge in regard to it.

In a lot of cases the it people are just following the rules and don’t know this.

Worse. If you are not in the USA, i.e., if NIST is not the correct authority, that insurer might actually be enforcing what the "correct" authority believes to be right, i.e., password expiration.

Maybe it wouldn't make a difference, but if I was the IT person telling users they have to change their passwords every 90 days, I would 100% include a line in the email blaming the insurance company.

I'm not in an IT dept (developer instead), but I'd bet money that would get you a thorough dressing down by an executive involved with the insurance. That sort of blaming goes over well with those at the bottom of the hierarchy, and poorly with those at the top.

The insurance people are not a part of the company, so I'm not sure who would be offended.

I wouldn't be mean about it. I'm imagining adding a line to the email such as:

> (Yes, I know this is annoying, but it's required by our insurance company.)

What is the insurance company going to do, jack up our rates because we accurately stated what their policy was?

The problem is that this particular insurance company was picked by someone who does work in yours.

This seems like a pretty awful place to work if my bosses have such fragile egos they can't handle me saying "our insurance requires us to do X". I'm not even really passing judgement on whether X is good or bad.

I'm not saying you're wrong, I've never worked in a company this large (except for a brief internship), or in IT specifically. But also, like, come on people, grow up.

You would probably have no idea what the requirement actually said or where it ultimately came from.

It would've gone from the insurer to the legal team, to the GRC team, to the enterprise security team, to the IT engineering team, to the IT support team, and then to the user.

Steps #1 to #4 can (and do) introduce their own requirements, or interpret other requirements in novel ways, and you'd be #5 in the chain.

"You never know..." is the worst form of security, and makes systems less secure overall. Passwords must be changed every month, just to be safe. They must be 20 alphanumeric characters (with 5 symbols of course), just to be safe. We must pass every 3-letter compliance standard with hundreds of pages of checklists for each. The server must have WAF enabled, because one of the checklists says so.

Ask the CIO what actual threat all this is preventing, and you'll get blank stares.

As an engineer what incentive is there to put effort into knowing where each form input goes and how to sanitize it in a way that makes sense? You are getting paid to check the box and move on, and every new hire quickly realizes that. Organizations like these aren't focused on improving security, they are focused on covering their ass after the breach happens.

> Ask the CIO what actual threat all this is preventing

the CIO is securing his job.

the CIO is securing his job.

Every CIO I have worked for (where n=3) has gotten where they are because they're a good manager, even though they have near-zero current technical knowledge.

The fetishizing of "business," in part through MBAs, has been detrimental to actually getting things done.

A century ago, if someone asked you what you do and you replied, "I'm a businessman. I have a degree in business," you'd get a response somewhere between "Yeah, but what to you actually do" and outright laughter.

It's a relatively recent change, too. Transition from "the executives and managers mostly came up through 10-25 years of doing 'lower' jobs in the company, and very much know how the business actually works" to "we hire MBAs to those roles directly" was throughout the '70s-'90s.

Finance and business grads have really taken over the economy, not just through technocratic "here's how to do stuff" advice but by personally taking all the reigns of power. They're even hard at work taking over medicine and pushing doctors out of the work-social upper-middle-class. Already did it with professors. Lawyers seem safe, so far.

They're taking over veterinary clinics too! The biggest owner of veterinary clinics is Mars inc. the candy company!

I wonder if Matt Levine has a bit about this

> Lawyers seem safe, so far.

Nope, lawyers are fucked too. It's just not as advanced yet: https://www.abajournal.com/web/article/arizona-approves-alte...

This looks like a variation of the Scunthorpe problem[1], where a filter is applied too naively, aggressively, and in this case, to the wrong content altogether. Applying the filter to "other stuff" sent to and among the servers might make sense, but there doesn't seem to be any security benefit to filtering actual text payload that's only going to be displayed as blog content. This seems like a pretty cut and dried bug to me.

1: https://en.wikipedia.org/wiki/Scunthorpe_problem

This is exactly what I was thinking as well, it's a great Scunthorpe example. Nothing from the body of a user article should ever be executed in any way. If blocking a list of strings is providing any security at all you're already in trouble because attackers will find a way around that specific block list.

> This looks like a variation of the Scunthorpe problem[1], where a filter is applied too naively

No.

> aggressively

No.

>, and in this case, to the wrong content altogether.

Yes - making it not a Scunthorpe problem.

Correct. And a great example of it.

I don't get why you'd have SQL injection filtering of input fields at the CDN level. Or any validation of input fields aside from length or maybe some simple type validation (number, date, etc). Your backend should be able to handle arbitrary byte content in input fields. Your backend shouldn't be vulnerable to SQL injection if not for a CDN layer that's doing pre-filtering.

Because someone said "we need security" and someone else said "what is security" and someone else said "SQL injection is security" and someone looked up SQL injections and saw the word "select" and "insert".

WAFs are always a bad idea (possible exception: in allow-but-audit mode). If you knew the vulnerabilities you'd protect against them in your application. If you don't know the vulnerabilities all you get is a fuzzy feeling that Someone Else is Taking Care of it, meanwhile the vulnerabilities are still there.

Maybe that's what companies pay for? The feeling?

WAFs can be a useful site of intervention during incidents or when high-severity vulns are first made public. It's not a replacement for fixing the vuln, that still has to happen, but it gives you a place to mitigate it that may be faster or simpler than deploying code changes.

> If you knew the vulnerabilities you'd protect against them in your application.

Correction: it is not your application but someone else's Certified Stuff (TM) that you can't change, but which is still vulnerable.

If your clients will let you pass the buck on security like this it would be very tempting to work towards the least onerous insurance metric and no further.

A simple reason would be if you're just using it as a proxy signal for bad bots and you want to reduce the load on your real servers and let them get rejected at the CDN level. Obvious SQL injection attempt = must be malicious bot = I don't want my servers wasting their time

> A simple reason would be if you're just using it as a proxy signal for bad bots

Who would be that stupid?

It should be thought of as defense-in-depth only. The backend had better be immune to SQL injection, but what if someone (whether in-house or vendor) messes that up?

I do wish it were possible to write the rules in a more context-sensitive way, maybe possible with some standards around payloads (if the WAF knows that an endpoint is accepting a specific structured format, and how escapes work in that format, it could relax accordingly). But that's probably a pipe dream. Since the backend could be doing anything, paranoid rulesets have to treat even escaped data as a potential issue and it's up to users to poke holes.

The farther a request makes it into infrastructure, the more resources it uses.

> I disagree with other posts here, it is partially a balance between security and usability. You never know what service was implemented with possible security exploits and being able to throw every WAF rule on top of your service does keep it more secure. Its just that those same rulesets are super annoying when you have a securely implemented service which needs to discuss technical concepts.

I might be out of the loop here, but it seems to me that any WAF that's triggered when the string "/etc/hosts" is literally anywhere in the content of a requested resource, is pretty obviously broken.

I don't think so. This rule for example probably block attacks on a dozen old WordPress vulnerabilities.

And a rule that denies everything blocks all vulnerabilities entirely.

A false positive from a conservative evaluation of a query parameter or header value is one thing, conceivably understandable. A false positive due to the content of a blog post is something else altogether.

This is a strawman, especially if like the parent claims this was improving security for one of the most popular website backends ever.

Rules like this might very well have had incredible positive impact on ten of thousands of websites at the cost of some weird debugging sessions for dozens of programmers (made up numbers obviously).

Look, any WAF that blocks a document like

    <!DOCTYPE html>
    <html lang="en">
    <body>
    <p>/etc/hosts is a file on Unix hosts</p>

> is pretty clearly broken

agree

> And you can't meaningfully measure product metrics like impact for fundamentally broken products

disagree

I have a WAF that blocks everything. It's obviously fundamentally broken, but in terms of product metrics like impact, it's incredible! It stops 100% of attacks!

Yup. Were a database company that needs to be compliant with SOC2, and I’ve had extremely long and tiring arguments with our auditor why we couldn’t adhere to some of these standard WAF rulesets because it broke our site (we allow people to spin up a demo env and trigger queries).

We changed auditors after that.

sounds like your security policy is wrong (or doesnt have a provision for exceptions managed by someone with authority to grant them), or your auditor was swerving out of his lane. As far as I've seen: SOC2 doesn't describe any hard security controls - it just asks to evaluate your policy versus your implemented controls.

You are absolutely correct, which is why we switched auditors. We use a third party to verify compliance of all our cloud resources (SecureFrame), and one of their checks is that specific AWS WAF rulesets are enabled on e.g. CloudFront endpoints. These are managed rulesets by AWS.

We disabled this check, auditor swerved out of his lane, I spent more several hours explaining things he didn’t understand, and things resolved after our CEO had a call with him (you can imagine how the discussion went).

All in all, if the auditor would have been more reasonable it wouldn’t have been an issue, but I’ve always been wary of managed firewall rulesets because of this reason.

There's no "trade-off" here. Blocking IPs that send "1337 h4x0r buzzword /etc/passwd" in it is completely naive and obtrusive, which is the modus operandi of the CDN being discussed here. There are plenty of other ways of hosting a website.

This is what surprises me in this story. I could not, at first glance, assume that either Substack people or Cloudflare people were incompetent.

Oh: I resisted tooth and nail about turning on a WAF at one of my gigs (there was no strict requirement for it, just cargo cult). Turns out - I was right.

> There is a temptation to just turn the rules off

Definitely, though I have seen other solutions, like inserting non-printable characters in the problematic strings (e.g. "/etc/ho<b></b>sts" or whatever, you get the idea). And honestly that seems like a reasonable, if somewhat annoying, workaround to me that still retains the protections.

Another silly workaround would be to take a screenshot of “/etc/hosts” and use images instead. Would break text browsers/reading mode though.

And accessibility.

> The people configuring WAF rules at CDNs tend to do a poor job understanding sites and services that discuss technical content. It's not just Cloudflare, Akamai has the same problem.

I agree. There is a business opportunity here. Right in the middle of your sentences.

Hint: Context-Aware WAF.

Many platforms have emerged in the last decade - some called it smart WAF, some called it nextgen WAF.. All vaporware garbage that consumes tons and tons of system resource and still manages to do a shit job of _actually_ WAF'ing web requests.

To be truly context-aware, you need to compute a priori about the situation - the user, the page, the interactions etc.

I've had the issue where filling out form fields for some company website triggers a WAF and then nobody in the company is able to connect me to the responsible party who can fix the WAF rules. So I'm just stuck.

In my experience the pain of false positives required to outweigh the "WAF is best practice" is just very very heigh. Most big businesses would rather lose/frustrate a small percentage of customers, to be "safe".

> The people configuring WAF rules at CDNs tend to do a poor job understanding sites and services that discuss technical content

They shouldn't be doing that job at all. The content of user data is none of their business.

100! [good] security just doesn't work as a mixing pattern... I'm not saying it's necessarily bad to use those additional protections but they come with severe limitations so the total value (as in cost/benefit) is hard to gauge.

I agree. From a product perspective, I would also support the decision. Should we make the rules more complex by default, potentially overlooking SQL injection vulnerabilities? Or should we blanket prohibit anything that even remotely resembles SQL, allowing those edge cases to figure it out?

I favor the latter approach. That group of Cloudflare users will understand the complexity of their use case accepting SQL in payloads and will be well-positioned to modify the default rules. They will know exactly where they want to allow SQL usage.

From Cloudflare’s perspective, it is virtually impossible to reliably cover every conceivable valid use of SQL, and it is likely 99% of websites won’t host SQL content.

If your web application is relying on Cloudflare filtration of input values to prevent SQL injection, your web application is vulnerable to SQL injection.

Defense in-depth. I would hope few would want a vulnerable web app and simply protect it via a WAF. But just because your web app is 'invulnerable' doesn't mean you should forgo the WAF.

But what is being defended against? This is blocking legitimate user behavior. Would it be defense in depth to also prohibit semicolons or two consecutive hyphen characters in all content? If your app is constructing paths to read from the server's filesystem based on substrings contained within client-provided field values, throwing an error if `"/etc/hosts"` appears in any input is not going to save you.

Unknown or unforeseen attacks. The WAF ruleset can be updated much faster than code. WAFs also provide flexibility in how requests are responded to, or even disallow access from IP ranges, certain browsers, etc.

WAFs do throw false positives and do require adjustments OOTB for most sites, but you’re missing the forest by focusing on this single case.

My defense in depth blocks Content-Length that's a prime number or divisible by 5. Can't be too safe!

What? If I construct my queries the right way (e.g., not concatenating strings together like it's the year 1990), then I never will want a WAF "helping" me by blocking my users because they have an apostrophe in their name.

That's a very narrow view of what a WAF does. You may want to review the OWASP ruleset at https://coreruleset.org/. However, this is just the ruleset. WAF vendors usually offer features above and beyond OWASP rule parsing.

And WAF rules can be tuned. There's no reason an apostrophe in a username or similar needs to be blocked, if it were by a rule.

Okay, I'll look at the "coreruleset" which you say is good.

Let's see what's blocked:

"Division by zero" anywhere in the response body since that's a php error. Good luck talking about math ([0] and [1])

Common substrings in webshells, all matched as strings in response bodies, rather than parsing HTML, so whatever, don't comment about webshells either [2]

Unless the body is compressed, in which case don't apply the above. Security [3].

Also, read this regex and tell me you understand what it's doing. Tell me the author of it understands what it matches: https://github.com/coreruleset/coreruleset/blob/943a6216edea...

What the coreruleset is doing here is trying to parse HTML, SQL, HTTP, and various other languages with Regular Expressions. This doesn't work. This will never give you a right result.

It's trying to keep up to date with the string representation of java and php errors, without even knowing the version of Java the server is running, and without the Java maintainers, who constantly add new errors, having any say.

The only reasons attackers aren't evading the webshell rules here trivially is because so few people use these rules in practice that they're not even worth defeating (and it is quite easy to have your php webshell generate unique html each load, which cannot be matched by a regular expression short of /.*/; html is not a regular grammar).

I was ready to see something that made WAFs feel like they did _anything_ based on your comment, but all I see is a pile of crap that I would not want anywhere near my site.

Filtering java error strings and php error strings out of my rust app's responses using regexes to parse html is just such a clown-world idea of security. Blocking the loading of web-shells until the attacker changes a single character in the 'title' block of the output html seems so dumb when my real problem is that someone could write an arbitrary executable to my server.

Every WAF ruleset I've read so far has made me sure it's a huge pile of snake-oil, and this one is no different.

[0]: https://github.com/coreruleset/coreruleset/blob/943a6216edea...

[1]: https://github.com/coreruleset/coreruleset/blob/943a6216edea...

[2]: https://github.com/coreruleset/coreruleset/blob/943a6216edea...

[3]: https://github.com/coreruleset/coreruleset/blob/943a6216edea...

The issue is you're picking out bits and pieces that /seem/ correct to you, but you don't seem to have experience defending a public website from intrusions.

These rules do in fact work. Like I've said previously, these rules require tuning for your particular website. If I'm "talking about math" then I would modify or disable that rule as needed.

I think this is the forest you're missing. WAF isn't "install it and walk away". WAF needs to be tested in conjunction with your release, like any other code would.

The WAF can and does protect against attacks your code would never think of. It also /logs requests/ in a way your web server will not, making it invaluable for auditing.

And when running 3rd party software that has a function you cannot control, but need to prevent, WAFs can do that, too. I have a particular query string that must work from an internal but not external network while external/internal users leverage the same URL -- WAF can do that with a custom rule examining the query string and denying access to the outside world.

Or if I need to prevent [AI] bot scraping. WAF can do that with a couple of clicks.

WAF also unloads the web server from malicious traffic. Instead of having to size up or out a web server, I can have a WAF appliance prevent that traffic from ever reaching the server.

> Every WAF ruleset I've read so far

You don't appear to have any experience with implementation or operation of a WAF, but are attempting to be authoritative and dismiss a WAFs utility.

> If I construct my queries the right way (e.g., not concatenating strings together like it's the year 1990)...

(in the anti-WAF camp but playing a pedant here)

In your Django app, you indeed follow the best practices and don't concatenate strings together and so think that this security theater doesn't apply. Yet, this is precisely how Django ORM works under the hood, and SQL injections are periodically found there.

The real solution here is to subscribe to the django-announce list and update Django, or backport the fix manually.

Sorry, we have to reject your comment due to security. The text "Cloudflare<apostrophe>s" is a potential SQL injection.

You know, I get the spirit of this criticism. But, specially in the age of AI, we're going to get thousands of barely reviewed websites on Cloudflare.

If you know what you're doing, turn these protections off. If you don't, there's one less hole out there.

In all seriousness, I don't see the justification for blocking "/etc/hosts" but allowing "'". The latter is probably a million times more likely to trigger a vulnerability.

The problem is that people who don't know what they are doing join the cargo cult and then impose these requirements on people who do know what they are doing.

Why not just whitelist the thousand most common words? That should be good enough for 99% of approriate content, and the smelly nerds who make websites or talk about them can take their tiny market segment and get bent.

Reminds me of an anecdote about an e-commerce platform: someone coded a leaky webshop, so their workaround was to watch if the string "OutOfMemoryException" shows up in the logs, and then restart the app.

Another developer in the team decided they wanted to log what customers searched for, so if someone typed in "OutOfMemoryException" in the search bar...

Careless analysis of free-form text logs is an underrated way to exploit systems. It's scary how much software blindly logs data without out of band escaping or sanitizing.

Why would someone "sanitize" OutOfMemoryException out of their logs? That is a silly point to make.

The point is not to sanitize known strings like "OutOfMemoryException". The point is to sanitize or (preferably) escape any untrusted data that gets logged, so that it won't be confused for something else.

i think GP's point is how would you even sanitize the string "OutOfMemoryException" which presumably comes from a trusted system

i guess demanding "Structured logs for everything or bust" is the answer? (i'm not a big o11y guy so pardon me if this is obvious)

"o11y" stands for "observability".

Numeronyms are evil and we should stop using them.

Thanks. My mind started running the random string generator given those restrictions, like a puzzle game. But had no idea of what it meant until you wrote it. Who invented that stupid idea and thought it would be a good one?

because its easily googlable.

counter point - people are going to use them, better to expose newbies early and often and then everyone is better off

shorthands will always be in demand. we used to say “horseless carriage”, then “automobile”, then “car”. would you rather use Light amplification by stimulated emission of radiation or just “laser”s? etc

in the new york times? sure, spell out observability. but on HN? come on. the term is 7 years old and is used all over the site. it’s earned it

Or we could use words that don't require people to use Google just to be able to read. A dependence on a search engine for reading text is unnecessary.

If you find typing tedious just use autocomplete or other tools instead of making it the readers' problem.

no we drive to work in our h16e to set up the l47n

I've never seen it before.

You're right, avoiding them gives better a11y

Yes, that's affirmatively aesthetically the best way to ensure artificiality automatically, or alternatively applicability and acceptability, there's appropriately a whole chapter about it in my autobiography, had to adventurously include it authentically (obviouslyyyyy).

t4s, couldn't agree more.

Low tech example: escape all newlines in user supplied strings, then add a known prefix to all user supplied data (let's say a double hashtag ##, but anything else works too). When you want to search logs for strings coming from your system, remove/ignore everything after the marker.

It all comes down to understanding whether the intersection of two grammars is empty.

The difficulty here is that in the example above, it's unlikely, given any amount of scale, that the two people were on the same team. They were doing different things with the same data and probably didn't know what the other was doing.

Sure you could add a convention to your 'how to log' doc that specifies that all user input should be tagged with double '#' but who reads docs until things break? convention is a shitty way to make things work.

There's 100 ways that you could make this work correctly. Only restarting on a much more specific string, i.e. including the app name in the log line etc . . . but that's all just reducing the likely hood that you get burned.

I've also written a OOM-Killer.sh myself, I'm not above that, but it's one of those edge cases that's impossible to do correctly, which is why parsing and acting on log data generally considered and anti-pattern.

An OutOfMemoryException log should not be the same as a search log

  Error: OutOfMemoryException

  Search: OutOfMemoryException

Until someone searches for "Error: OutOfMemoryException"

If structured logging is too much, unique prefixes solve this issue. Basically you need some token that user provided data is unable to output to the log. If you rigorously escape all newlines, you can then use start-of-line and end-of-line as unforgeable tokens. The possibilities are endless and it all comes down to understanding whether the intersection of two grammars is empty.

I read the gp to mean that error.log (being parsed to look for OOM) would have no associations with userSearches.log, in which an end-user searched for OOM

Absolutely incredible how dense HN can be and that no one has explained. Obviously that isn’t what they are saying, they are saying it’s profoundly stupid to have the server be controlled by a simple string search at all.

I've actually gone through this a few times with our WAF. A user got IP-banned because the WAF thought a note with the string "system(..." was PHP injection.

Does it block `/etc//hosts` or `/etc/./hosts`? This is a ridiculous kind of whack-a-mole that's doomed to failure. The people who wrote these should realize that hackers are smarter and more determined than they are and you should only rely on proven security, like not executing untrusted input.

Yeah, and this seems like a common Fortune 500 mandatory checkbox. Gotta have a Web Application Firewall! Doesn't matter what the rules are, as long as there are a few. Once I was told I needed one to prevent SQL injection attacks... against an application that didn't use an SQL database.

If you push back you'll always get a lecture on "defense in depth", and then they really look at you like you're crazy when you suggest that it's more effective to get up, tap your desk once, and spin around in a circle three times every Thursday morning. I don't know... I do this every Thursday and I've never been hacked. Defense in depth, right? It can't hurt...

I’m going through exactly this joy with a client right now.

“We need SQL injection rules in the WAF”

“But we don’t have an SQL database”

“But we need to protect against the possibility of partnering with another company that needs to use the same datasets and wants to import them into a SQL database”

In fairness, these people are just trying to do their job too. They get told by NIST (et al) and Cloud service providers that WAF is best practice. So it’s no wonder they’d trust these snake oil salesman over the developers who asking not to do something “security” related.

If they want to do their job well, how about adding some thinking into the mix, for good measure? Good would also be,if they actually knew what they are talking about, before trying to tell the engineers what to do.

> If they want to do their job well, how about adding some thinking into the mix, for good measure?

That’s what the conversation I shared is demonstrating ;)

> Good would also be,if they actually knew what they are talking about, before trying to tell the engineers what to do.

Often the people enduring the rules aren’t supposed to be security specialists. Because you’ll have your SMEs (subject matter experts) and your stockholders. The stakeholders will typically be project managers or senior management (for example) who have different skill sets and priorities to the SMEs.

The problem is that when it comes to security, it’s a complicated field where caution is better than lack of caution. So if a particular project does call on following enhanced secret practices, it becomes a ripe field for snake oil salesman.

Or to put it another way: no company would get sued for following security theatre but they are held accountable if there is a breach due to not following security best practices.

So often it doesn’t matter how logical and sensible the counter argument is, it’s automatically a losing argument

They don't want to do their job well. They want to look like they're doing their job well, to people who don't know how to do the job and whose metrics are completely divorced from actual merit.

That’s a common misconception taken from an engineers perspective but you have to understand their job isn’t about engineering, it’s about risk mitigation. And when viewed from that perspective, they are doing their job.

The real problem is that the domain has gotten so complicated that a traditional risk mitigation approach to is an outdated role and is now better fulfilled by technical staff who specialise in security. But that’s an organisation problem caused by senior management (C-suite and above) rather than a particular individual in that specific role not doing their job well.

I love that having a web application firewall set to allow EVERYTHING passes the checkbox requirement ...

(I’m in the anti-WAF camp) That does stand to improve your posture by giving you the ability to quickly apply duct tape to mitigate an active mild denial of service attack. It’s not utterly useless.

Denial of service prevention and throttling of heavy users is a fine use, searching for a list of certain byte strings inside input fields and denying requests that contain them isn't.

Doesn't it also add latency to every request?

So does running McAfee on every POST body but some places really wanna do that regardless. (I at least hope the scanner isn't running in the kernel for this one).

Yeah, we were asked to do this at my last job by some sort of security review. This one doesn't bother me as much. "Display 'network error' whenever a user uploads a file containing 'SELECT *'" is a bad user experience. "Some files in this repository have been flagged as containing a virus and are not visible in the web interface until allowed by an administrator," is OK with me, though.

I think the main point is the WAF companies must have lobbied to get that into the checklist

the main point is you need to pay a third party

You can call your existing reverse proxy a WAF to check this checklist item. (Your point still stands, on the median companies may opt to purchase a WAF for various reasons.)

Often it is just pushing responsibility.

sure but how much? 3-10ms is fine for the fast protection when shit hits the fan.

[dead]

A large investment bank I worked for blocked every URL that ended in `.go`. Considering I mostly wrote Golang code it was somewhat frustrating.

See "enumerating badness" as a losing strategy. I knew this was a bad idea about 5 minutes after starting my first job in 1995.

Well I've just created an account on substack to test this but turns out they've already fixed the issue (or turned off their WAF completely)

How would that be hard? Getting the absolute path of a string is in almost all languages stdlibs[1]. You can just grep for any string containing slashes and try resolve them and voilá

Resolving wildcards is trickier but definitely possible if you have a list of forbidden files

[1]: https://nodejs.org/api/path.html#pathresolvepaths

Edit: changed link because C's realpath has a slightly different behavior

The reason it's doomed to failure is because WAFs operate before your application, and don't have any clue what the data is.

Here is a WAF matching line: https://github.com/coreruleset/coreruleset/blob/943a6216edea...

Here's where that file is loaded: https://github.com/coreruleset/coreruleset/blob/943a6216edea...

It's loaded with '"@pmFromFile lfi-os-files.data"' which means "case-insensitive match of values from a file".

So yeah, the reason it can't resolve paths properly is because WAFs are just regex and substring matching trying to paper over security issues in an application which can only be solved correctly at the application level.

It’s not hard, but I think that’s more computation than a CDN should be doing on the edge. If your CDN layer is doing path resolution on all strings with slashes, that’s already some heavy lifting for a proxy layer.

> How would that be hard? Getting the absolute path of a string is in almost all languages stdlibs[1]. You can just grep for any string containing slashes and try resolve them and voilá

Be very, very careful about this, because if you aren't, this can actually result in platform-dependent behavior or actual filesystem access. They are bytes containing funny slashes and dots, so process them as such.

Edit: s/text/bytes/

Is a security solution worthless if it can't stop a dedicated attacker? A lot of WAF rules are blocking probes from off-the-shelf vulnerability scanners.

"It's technically better than nothing," is kind of a bizarre metric.

It's like not allowing the filesystem to use the word "virus" in a file name. Yes, it technically protects against some viruses, but it's really not very difficult to avoid while being a significant problem to a fair number of users with a legitimate use case.

It's not that it's useless. It's that it's stupid.

Do you lock your front door?

Do you brace yours with a bar?

No, but even a steel bar would only slow down a determined thief...so I guess it's worthless?

It's merely security theater.

It reminds me of when airports started scanning people's shoes because an attacker had used a shoe bomb. Yes, that'll stop an attacker trying a shoe bomb again, but it disadvantages every traveller and attackers know to put explosives elsewhere.

“attacker had used a shoe bomb”

It’s even dumber than that. An attacker tried and failed to use a shoe bomb, and yet his failure has caused untold hours of useless delay for over 13 years now.

Now you have to buy your liberty with pre-check.

Most ransomware attacks are opportunistic. They scan basically the whole internet for vulnerabilities and attack from there. It's usually not a skilled attacker targeting a specific company.

Ransomware is a huge and growing problem. Very different than airline security, where attacks are extremely uncommon. If planes were constantly getting blown up, and if a majority of those attacks started with a shoe bomb, then checking everyone's shoes would seem a lot more reasonable, no?

IMHO the primary value for WAFs is for quickly blocking known vulnerabilities with specific rules to mitigate vulnerabilities while they are being properly patched. Ideally the WAF knows what software is behind it (example WordPress, Java app, ...) and can apply filters that may be relevant.

Anything else is just a fuzzy bug injector that will only stop the simplest scanners and script kiddies if you are lucky.

Every security solution can only stop a certain fraction of attacks.

No one expects any WAF to be a 100% solution that catches all exfiltration attempts ever, and it should not be treated this way. But having it is generally better than not having it.

> But having it is generally better than not having it.

The problem is that generally you're breaking actual valid use cases as the tradeoff to being another layer of defense against hypothetical vulnerabilities.

Yes, discussing the hosts file is a valid use case.

Yes putting angle brackets in the title of your message is valid use case your users are going to want.

Yes putting "mismatched" single quotes inside double quotes is a thing users will do.

Yes your users are going to use backslashes and omit spaces in a way that looks like attempts at escaping characters.

(All real problems I've seen caused by overzealous security products)

"But having it is generally better than not having it."

I believe the exact opposite.

One (of many) reasons is that it can make your code less secure, by hiding your security mistakes from you.

If your WAF obscures escaping issues during your own testing and usage you could very easily let those escaping issues go unresolved - leaving you vulnerable to any creative attacker who can outsmart your WAF.

If you are in charge of testing code for escaping issues, and you do that through a WAF, you might not be very good at your job.

> But having it is generally better than not having it.

So is HN and every other site in the world insecure because it allows users to post "/etc/hosts" ?

Maybe? I don't know nor care. Assuming that HN has a vuln with path traversal, a sanely configured WAF would block the traversal attempt.

I propose someone who doesn’t know or care how a system works shouldn’t be prescribing what to do to make it secure. Otherwise this is like suggesting every gate must have a lock to be secure, even those which aren’t connected to any walls.

https://i.imgur.com/ntYUQB1.jpeg

> someone who doesn’t know or care how a system works shouldn’t be prescribing what to do to make it secure

The part that’s not said outloud is that a lot of “computer security” people aren’t concerned with understanding the system. If they were, they’d be engineers. They’re trying to secure it without understanding it.

Good computer security people are engineers.

*some traversal attempts

Is it? The WAF is also now an attack surface itself, and I don't think WAFs have exactly proven themselves as something that meaningfully increases security. They certainly break things unpredictably, though.

> But having it is generally better than not having it.

Why? It obviously has an annoying cost and equally obviously won't stop any hacker with a lukewarm IQ

No, that logic doesn't follow. If your application is so hopelessly vulnerable as to benefit from such naive filtering of the text "/etc/hosts, then your application is still going to be vulnerable in precisely the same ways, with just slightly modified inputs.

It is net zero for security and net negative for user experience, so having it is worse than not having it.

Net zero for security might be generous.

The way I assume it works in practice on a real team is that after some time, most of your team will have no idea how the WAF works and what it protects against, where and how it is configured… but they know it exists, so they will no longer pay attention to security because “we have a tool for that”, especially when they should have finished that feature a week ago…

Dropping 0.5% of requests will prevent even the most sophisticated attacks (think APT!). Sometimes.

Dropping 95% is even more secure, plus it lives the lucky few that get past it a sense of pride and exclusivity.

Is that like a "sense of pride and accomplishment"?

https://knowyourmeme.com/memes/events/star-wars-battlefront-...

"How could Substack improve this situation for technical writers?"

How about this: don't run a dumb as rocks Web Application Firewall on an endpoint where people are editing articles that could be about any topic, including discussing the kind of strings that might trigger a dumb as rocks WAF.

This is like when forums about web development implement XSS filters that prevent their members from talking about XSS!

Learn to escape content properly instead.

I'm in the position where I have to run a WAF to pass security certifications. The only open source WAFs are modsecurity and it's beta successor, coraza. These things are dumb, they just use OWASP's coreruleset which is a big pile of unreadable garbage.

Surprisingly simple solution

hire a cybersec person. I don't think they one.

> This case highlights an interesting tension in web security: the balance between protection and usability.

But it doesn't. This case highlights a bug, a stupid bug. This case highlights that people who should know better, don't!

The tension between security and usability is real but this is not it. Tension between security and usability is usually a tradeoff. When you implement good security that inconveniences the user. From simple things like 2FA to locking out the user after 3 failed attempts. Rate limiting to prevent DoS. It's a tradeoff. You increase security to degrade user experience. Or you decrease security to increase user experience.

This is neither. This is both bad security and bad user experience. What's the tension?

I would say it’s a useful security practice in general to apply WAF as a blanket rule to all endpoints and then remove it selectively when issues like this occur. It’s much, much, harder to evaluate every single public facing endpoint especially when hosting third party software like Wordpress with plugins.

Precisely.

This also reminded me, I think in the PHP 3 era, PHP used to "sanitize" the contents of URL requests to blanket combat SQL injections, or perhaps, it was a configuration setting that would be frequently turned on in shared hosting services. This, of course, would've been very soon discovered by the authors of the PHP site and various techniques were employed to circumvent this restriction, overall giving probably even worse outcomes than if the "sanitation" wasn't there to begin with.

The days of addslashes() and stripslashes()!

After having been bitten once (was teaching a competitive programming team, half the class got a blank page when submitting solutions, after an hour of debugging I narrowed it down to a few C++ types and keywords that cause 403 if they appear in the code, all of which happen to have meaning in Javascript), and again (working for a bank, we had an API that you're supposed to submit a python file to, and most python files would result in 403 but short ones wouldn't... a few hours of debugging and I narrowed it down to a keyword that sometimes appears in the code) and then again a few months later (same thing, new cloud environment, few hours burned on debugging[1]), I had the solution to his problem in mind _immediately_ when I saw the words "network error".

[1] the second time it happened, a colleague added "if we got 403, print "HAHAHA YOU'VE BEEN WAFFED" to our deployment script, and for that I am forever thankful because I saw that error more times than I expected

Do you remember if that was Cloudflare or some other likely WAF?

First time something on-prem, maybe F5. Second time AWS.

Oh, I just remembered I had another encounter with the AWS WAF.

I had a Jenkins instance in our cloud account that I was trying to integrate with VSTS (imagine github except developed by Microsoft, and still maintained, nevermind that they own github and it's undoubtedly a better product). Whenever I tried to trigger a build, it worked, but when VSTS did, it failed. Using a REST monitor service I was able to record the exact requests VSTS was making and prove that they work with curl from my machine... after a few nights of experimenting and diffing I noticed a difference between the request VSTS made to the REST monitor and my reproduction with curl: VSTS didn't send a "User-Agent" header, so curl supplied one by default unless I added I think -H "User-Agent:", and therefore did not trigger the first default rule in the AWS WAF, "if your request doesn't list a user agent you're a hacker".

HAHAHA I'VE BEEN WAFFED AGAIN.

+++ATH

We faced a similar issue in our application. Our internal Red Team was publishing data with XSS and other injection attack attempts. The attacks themselves didn't work, but the presence of these entries caused our internal admin page to stop loading because our corporate firewall was blocking the network requests with those payloads in them. So an unsuccessful XSS attack became an effective DoS attack instead.

This is funny and sad at the same time.

Everything old is new again :) We used to call this the Scunthorpe problem.

https://en.m.wikipedia.org/wiki/Scunthorpe_problem

I remember back in the old days on the Eve Online forums when the word cockpit would always turn up as "c***pit". I was quite amused by that.

This is actually a better solution, replacing dangerous words with placeholders, instead of blocking the whole payload. That at least gives the user some indication of what is going on. Not that I'm for any such WAF filters in the first place, just if having to choose between the lesser of two evils I'd choose the more informative.

Not so sure. Imagine you have a base64 encoded payload and it just happens to encode the forbidden word. Good luck debugging that, if the payload only gets silently modified.

I suddenly understand why it makes sense to integrity-check a payload that is already protected by all three of TLS, TCP checksum and CRC.

Good point, i take take that back. Having payload mutated would indeed be even more scary. Even more so if it actually contains real queries, imagine what could happen if /etc/hosts becomes /etc/*.

See also: Recent scrubbing US government web sites for words like "diversity", "equity", and "inclusion".

Writing about biology, finance, or geology? Shrug.

Dumb filtering is bad enough when used by smart people with good intent.

Huh, quick tell one Musk's DOGE l33t h4ck3ers about reverse proxies, and put all government sites behind one, that looks for those words and returns an error... Error 451 would be the most appropriate!

For bonus, the reverse proxy will run on a system infiltrated by Russian (why not Chinese as well) hackers.

It is time to add the Substack case to this Wikipedia article.

"I wonder why it's called Scunthorpe....?"

sits quietly for a second

"Oh nnnnnnnooooooooooooooo lol!"

I ran into a similar issue with OpenRouter last night. OpenRouter is a “switchboard” style service that provides a single endpoint from which you can use many different LLMs. It’s great, but last night I started to try using it to see what models are good at processing raw HTML in various ways.

It turns out OpenRouter’s API is protected by Cloudflare and something about specific raw chunks of HTML and JavaScript in the POST request body cause it to block many, though not all, requests. Going direct to OpenAI or Anthropic with the same prompts is fine. I wouldn’t mind but these are billable requests to commercial models and not OpenRouter’s free models (which I expect to be heavily protected from abuse).

Did you report it?

Not yet, other than on X, because the project's comms is oriented around Discord which involves some hoop jumping.

(Update: On the way to doing that, I decided to run my tests again and they now work without Cloudflare being touchy, so I'll keep an eye on it!)

(Update 2: They just replied to me on X and said they had fixed their Cloudflare config - happy days!)

I encountered this a while ago and it was incredibly frustrating. The "Network error" prevented me from updating a post I had written for months because I couldn't figure out why my edits (which extended the length and which I assumed was the problem) couldn't get through.

Trying to contact support was difficult too due to AI chatbots, but when I finally did reach a human, their "tech support" obviously didn't bother to look at this in any reasonable timeframe.

It wasn't until some random person on Twitter suggested the possibility of some magic string tripping over some stupid security logic that I found the problem and could finally edit my post.

> This case highlights an interesting tension in web security: the balance between protection and usability.

This isn't a tension. This rule should not be applied at the WAF level. It doesn't know that this field is safe from $whatever injection attacks. But the substack backend does. Remove the rule from the WAF (and add it to the backend, where it belongs) and you are just as secure and much more usable. No tension.

I would say it’s a decent security practice to apply WAF as a blanket rule to all endpoints and then remove it selectively when issues like this occur. It’s much, much, harder to evaluate every single public facing endpoint especially when hosting third party software like Wordpress with plugins.

I don't agree. WAFs usually add more attack surface than they remove.

https://www.macchaffee.com/blog/2023/wafs/

Of course, Wordpress is basically undefendable, so I'd never ever host it on a machine that has anything else of value (including e.g. db credentials that give access to much more than the public content on the WP installation).

There is a tension, but it's between paying enough to developers to actually produce decent code or pay a 3rd-party to firewall the application.

Again, there is no tension.

People will manage to circumvent the firewall if they want to attack your site. But you will still pay, and get both the DoS vulnerabilities created by the firewall and the new attack vectors in the firewall itself.

WAFs were created by people who read https://thedailywtf.com/articles/Injection_Rejection and didn't realize that TDWTF isn't a collection of best practices.

Content filtering should be highly context dependent. If the WAF is detached from what it's supposed to filter, this happens. If the WAF doesn't have the ability to discern between command and content contexts, then the filtering shouldn't be done via WAF.

This is like spam filtering. I'm an anti-spam advocate, so the idea that most people can't discuss spam because even the discussion will set off filters is quite old to me.

People who apologize for email content filtering usually say that spam would be out of control if they didn't have that in place, in spite of no personal experience on their end testing different kinds of filtering.

My email servers filter based on the sending server's configuration: does the EHLO / HELO string resolve in DNS? Does it resolve back to the connecting IP? Does the reverse DNS name resolve to the same IP? Does the delivery have proper SPF / DKIM? Et cetera.

My delivery-based filtering works worlds better than content-based filtering, plus I don't have to constantly update it. Each kind has advantages, but I'd rather occasional spam with no false positives than the chance I'm blocking email because someone used the wrong words.

With web sites and WAF, I think the same applies, and I can understand when people have a small site and don't know or don't have the resources to fix things at the actual content level, but the people running a site like Substack really should know better.

Yes to smart filtering at the right layer. The whole reverse DNS checks et al. are so effective. I recently moved my personal mailbox from a host who didn't do these kinds of checks to one that does. My received spam volume instantly went from about 20 a day (across all my aliases) to less than 1 a week.

SPF and DKIM are now more commonly implemented correctly by spammers than by major email providers.

https://news.ycombinator.com/item?id=43468995

Yes, but they are still effective at preventing spam from spammers who are pretending to be others.

Few years ago I had an application that allowed me to set any password, but then gave mysterious errors when I tried to use that password to login. Took me a bit to figure out what was going on, but their WAF blocked my "hacking attempt" of using a ' in the password.

The same application also stored my full password in localStorage and a cookie (without httponly or secure). Because reasons. Sigh.

I'm going to do a hot take and say that WAFs are bollocks mainly used by garbage software. I'm not saying a good developer can't make a mistake and write a path traversal, but if you're really worried about that then there are better ways to prevent that than this approach which obviously is going to negatively impact users in weird and mysterious ways. It's like the naïve /(fuck|shit|...)/g-type "bad word filter". It shows a fundamental lack of care and/or competency.

Aside: is anyone still storing passwords in /etc/passwd? Storing the password in a different root-only file (/etc/shadow, /etc/master.passwd, etc.) has been a thing on every major system since the 90s AFAIK?

It's more that /etc/hosts and /etc/passwd are good for testing because they always exist with predictable contents on almost every system. If you inject "cat /etc/passwd" to various URLs you can grep for "root:" to see if it worked.

So it's really blocking doorknob-twisting scripts.

Oh yeah, I've used it for that purpose. Seems rather silly to block that outright though since you can use many commonly distributed files.

my bank requires non-alphanumeric characters in their passwords but will reject a password if it has alphanumeric characters it associates with command injection attacks.

as far as WAFs being garbage, they absolutely are, but this is a great time for a POSIWID analysis. A WAF says its purpose is to secure web apps. It doesn't do that, but people keep buying them. Now we're faced with a crossroads: we either have to assume that everyone is stupid or that the actual purpose of a WAF is something other than its stated purpose. I personally only assume stupidity as a last resort. I find it lazy and cynical, and it's often used to dismiss things as hopeless when they're not actually hopeless. To just say "Oh well, people are dumb" is a thought-terminating cliche that ignores potential opportunities. So we do the other thing and actually take some time to think about who decides to put a WAF in-place and what value it adds for them. Once you do that, you see myriad benefits because a WAF is a cheap, quick solution that allows non-technical people to say they're doing something. You're the manager of a finance OU that has a development group in it whose responsibility is some small web app. Your boss just read an article about cyber security and wants to know what this group two levels below you is doing about cyber security. Would you rather come back with "We're gonna need a year, $1 million and every other dev priority to be pushed back in order to develop a custom solution" or "We can have one fired up tomorrow for $300/mo, it's developed and supported by Microsoft and it's basically industry standard." The negative impact of these things is obvious to us because this is what we do, but we're not always the decision-makers for stuff like that. Often the decision-makers are actually that naive and/or they're motivated less by the ostensible goal of better web app security and more by the goal of better job security.

As far as etc/passwd you're right that passwords don't live there anymore but user IDs often do and those can indicate which services are running as daemons on a given system. This is vital because if you can figure out what services are running you can start version fingerprinting them and then cross-referencing those versions with the CVE database.

I understand applying path filters in URLS and search strings, but I find it odd that they would apply the same rules to request body content, especially content encoded as valid JSON, and especially for a BLOG platform where the content would be anything.

Indeed a severe case of paranoia?

1. Create a new post. 2. Include an Image, set filter to All File types and select "/etc/hosts". 3. You get served with an weird error message box displacing a weird error message. 4. After this the Substack posts editor is broken. Heck, every time i access the Dashboard, it waits forever to build the page.

Did find this text while browsing the source for an error (see original ascii art: https://pastebin.com/iBDsuer7):

SUBSTACK WANTS YOU

TO BUILD A BETTER BUSINESS MODEL FOR WRITING

                   https://substack.com/jobs

"Who signed off on your WAF rules" would be a great reverse interview question then.

This looks like it was caused by this update https://developers.cloudflare.com/waf/change-log/2025-04-22/ rule 100741.

It references this CVE https://github.com/tuo4n8/CVE-2023-22047 which allows the reading of system files. The example given shows them reading /etc/passwd

AFAICT it's also (though I'm very rusty) in ModSecurity, if XML content processing is enabled then rules like these will trip:

    SecRule REQUEST_COOKIES|!REQUEST_COOKIES:/__utm/|REQUEST_COOKIES_NAMES|ARGS_NAMES|ARGS|XML:/* "@pmFromFile lfi-os-files.data"
    SecRule REQUEST_COOKIES|!REQUEST_COOKIES:/__utm/|REQUEST_COOKIES_NAMES|ARGS_NAMES|ARGS|XML:/* "@pmFromFile unix-shell.data" ...

The advantage (whack-a-mole notwithstanding) of a WAF is it orders of magnitude easier to tweak WAF rules than upgrade say, Weblogic, or other teetering piles of middleware.

So that's why immediately when I hear "WAF" I read "...and the site will break in weird and exciting ways due to arbitrary, badly developed heuristics outside of your control, every odd day of every even week" - I remember the glory days of shared hosting and mod_security.

Turns out the hunches were right all along.

https://en.wikipedia.org/wiki/Bush_hid_the_facts

The problem with WAF is discussed in https://users.ece.cmu.edu/~adrian/731-sp04/readings/Ptacek-N....

One of the authors of the paper has said "WAFs are just speed bump to a determined attacker."

> "WAFs are just speed bump to a determined attacker."

We wish. Speed bumps don't totally immobilise a pseudo-random selection of innocent vehicles.

Locks are a speedbump for a lockpick.

Doors are a speedbump for a car.

Well yeah, sure, doesn't mean I'm going to have an open doorframe or a door without a lock.

The difference is that a door tends to be the only thing between you and an attacker. A speedbump is better than nothing.

This isn't like having a lock on your door, this is like having a cheap, easily pickable padlock on your bank vault. If the vault has a proper lock then the padlock serves no purpose, and if it doesn't then you're screwed regardless.

I think a WAF is closer to a component of an entry control point, like on a military base. It's a tool for manned security to interact with and inspect traffic. Unmanned, they're just an obstacle to route around, but manned, they're an effective way to provide asymmetries to the defender.

WAFs can have thousands of rules ranging from basic to the sophisticated, not unlike mechanisms you can deploy at a checkpoint.

Security devices like IDSes or WAFs allow deploying filtering logic without touching an app directly, which can be hard/slow across team boundaries. They can allow retroactive analysis and flagging to a central log analysis team. Being able to investigate whether an adversary came through your door after the fact is powerful, you might even be able to detect a breach if you can filter through enough alerts.

People are more likely to get dismissed for not installing an IDS or WAF than having one. Its effectiveness is orthogonal to the politics of its existence, most of the time.

And to extend the metaphor to cover the false positives these systems produce, sometimes the padlock seizes shut if the air temperature is in a certain range, and the team that put it there refuses to take responsibility for the fact they've locked your customers from accessing their assets with the valid key.

I have a lifetime Pastebin account that I hadn't used for some years. Last year I enrolled in a "linux administration" class and tried to use that pastebin (famous for sharing code) to share some code/configurations with other students. When I tried to paste my homework I kept getting a Cloudflare error page. I don't even remember what I was pasting, but it was normal linux stuff. I contacted pastebin support - of course I got ghosted.

I am sharing this in relation to the WAF comments and how much the companies implementing WAF care about your case.

As a card carrying Substack hater, I’m not suprised.

> "How could Substack improve this situation for technical writers?"

They don’t care about (technical) writers. All they care about is building a TikTok clone to “drive discoverability” and make the attention-metrics go up. Chris Best is memeing about it on his own platform. Very gross.

Reminds me of Slashdot and breaking the page by widening it with certain characters

We briefly had a WAF forced upon us and it caused so many problems like this we were able to turn it off, for now. I'm sure it'll be back.

Could this be trivially solved client-side by the editor if it just encoded the slashes, assuming it's HTML or markdown that's stored? Replacing `/etc/hosts` with `&#47;etc&#47;hosts` for storage seems like an okay workaround. Potentially even doing so for anything that's added to the WAF rules automatically by syncing the rules to the editor code.

It's something I ran into quite a few times in my career. It's a weird call to get if the client can't save their cms site, due to typing something harmless. I think worst was when there was a dropdown that I defined which had a value in the mod rules that was not allowed.

I cannot reproduce this.

That reminds me of issues I once had with Microsoft's boneheaded WAF. We had base64 encoded data in a cookie, and whenever certain particular characters were produced next to each other in the data - I think the most common was "--" - the WAF would tilt and stop the "attempted SQL injection attack". So every so often someone would get an illegal login cookie and just get locked out of the system until they deleted it or it expired. Took a while to find out what went wrong, and even longer to figure out how to remove the more boneheaded rules from the WAF.

Between around 2005 and 2011 in France, if a child was born and parents Mr Bar and Mrs Baz wanted to transmit both of their last names, he or she had to be named "Foo Bar--Baz". No, that's not a typo, that's two hyphens. Check out "Circulaire du 6 décembre 2004 relative au nom de famille" if you don't believe me.

Yes, the people in charge probably didn't think or know of SQL comments. However, it worked well as long as input is sanitized and not concatenated, which is often the case using modern frameworks or common sense.

However, nowadays, we just put a WAF in front of everything, it's cheaper that way because common sense is hard to come by. People like Foo Bar--Baz still exist, and unless they've had their name changed, they're sometimes running into extremely wierd issues in the web software they're using.

At least, in this case, the WAF in question had the decency to return 403.

I've worked with a WAF installation (totally different product), where the "WAF fail" tell was HTTP status 200 (!) and "location: /" (and some garbage cookies), possibly to get browsers to redirect using said cookies. This was part of the CSRF protection. Other problems were with "command injection"-patterns (like in the article, expect with specific Windows commands, too - they clash with everyday words which the users submit), and obviously SQL injections which cover some relevant words, too.

The bottom line is that WAFs in their "hardened/insurance friendly" standard configs are set up to protect the company from amateurs exposing buggy, unsupported software or architectures. WAF's are useful for that, but you still gave all the other issues with buggy, unsupported software.

As others have written, WAFs can be useful to protect against emerging threats, like we saw with the log4j exploit which CloudFlare rolled out protection for quite fast.

Unless you want compliance more than customers, you MUST at least have a process to add exceptions to "all the rules"-circus they put in front of the buggy apps.

Whack-a-mole security filtering is bad, but whack-a-mole relaxation rule creation against an unknown filter is really tiring.

Almost equally fun are the ones that simply drop the connection and leave you waiting for a timeout.

it was a cf managed waf rule for a vulnerability that doesn't apply to us. we've disabled it.

This comment deserves to be much higher, assuming this user speaks for Substack (no previous submissions or comments, but the comment implies it).

i don't speak for substack, but i do work there and changed the WAF rule :)

Why not review rules before applying them?

Seems like a case of somebody installing something they couldn’t be bothered to understand to tick a box marked security.

The outcome is the usual one, stuff breaks and there is no additional security.

As soon as I saw the headline, I knew this was due to a WAF.

I worked on a project where we had to use a WAF for compliance reasons. It was a game of wack-a-mole to fix all the places where standard rules broke the application or blocked legitimate requests.

One notable, and related example is any request with the string "../" was blocked, because it might be a path traversal attack. Of course, it is more common that someone just put a relative path in their document.

Weird idea: What if user content was stored and transmitted encrypted by default? Then an attacker would have to either (a) identify a plaintext which encrypts to an attack ciphertext (annoying, and also you could keep your WAF rules operational for the ciphertext, with minimal inconvenience to users) or (b) attack the system when plaintext is being handled (could still dramatically reduce attack surface).

> For now, I'll continue using workarounds like "/etc/h*sts" (with quotes) or alternative spellings when discussing system paths in my Substack posts.

Ahh, the modern trend of ”unalived”¹ etc. comes to every corner of society eventually.

1. <https://knowyourmeme.com/memes/unalive>

It's /con/con all over again

I don't get it. Why aren't those files just protected so they have no read or write permissions? Isn't this like the standard way to do things? Put the blog in a private user space with minimal permissions.

Why would random text be parsed? I read the article but this doesn't make sense to me. They suggested directory transversal but your text shouldn't have anything to do with that and transversal is solved by permission settings

this is the usual approach with web application firewalls, block all the 100500 known attacks. Doesn't matter if they are not applicable to your website. Some of them are obviously OS-depended (having .exe in the URLs) but it doesn't matter, it's blocked just in case

I do understand this appoach. From the defence point of view it makes sense, if you have to create a solution to protect millions of websites it doesn't make sense to tailor it to specifics of a single one

Can you help me understand the exploit here? I'd really like to understand.

(What's below is written not as "this is how it should be done" but instead "what I understand should be done". To provide context to what I do and do not understand so that my misunderstandings can be more directly addressed)

I understand being over zealous, an abundance of caution. But what I'm confused about is why normal text could lead to an exploit in the first place. I can only understand this being a problem if arbitrary text is being executed. Which that would appear to be a HUGE security hole ripe for exploitation. But path access is handled by privileges. So even if arbitrary text is being executed, how can that lead to exploitation without already having a major security hole?

Maybe I'm not understanding substack? I've only been a reader. But why is the writer not in a container or chroot? If you want you be overly zealous why not use two vms? Put them in a vm to write, once they've edited then run tests and then use that as the image for the userspace in the ephemeral vm that is viewed by readers. Would this still be exploitable? I don't mean image for the whole vm, I really do mean a subimage so you can lock that up.

Misconfiguring your web server such that example.com/../../etc/passwd returned the actual file was a common vulnerability in the early 00s. Or cgi scripts that worked with real file paths but accepted any path

WAFs blocking the string with the filename then is the "to make sure nobody ever accidentally leaves your gate open, we've replaced it with a concrete wall" solution to this problem. You might never have this problem, and might need to actually use the gate but the vendor/security team has successfully solved their problem of checking off a blocked attack, and the consequences are now your problem

  > directory transversal attack

I asked why setting permissions was not a sufficient solution. Is someone gaining root? How?

I understand there's the user visiting substack and the person editing on substack. Certainly this is about the person editing. This is why I asked about the containerization side. That's an extra layer in permissions. Not only should that editor not have permissions to edit `/etc/passwd` (or some other file), but they wouldn't be able to do so even if gaining root. They'd need to gain root, break out of the container, and gain root again (hopefully that container is being run as a user and not root!).

But even there, I'm still confused about the exploits. How is a transversal even happening? Why is text even being executed? I understand we're sending POST requests but why is that POST request able to do anything other than input string literals into a text body? Isn't this a prepared statement? Why does that POST request have permission to access those files in the first place? Like even if a malicious editor circumvented defenses and was able to write injections, accessing those files shouldn't be possible from permissions, right?

My understanding is that for this solution to be effective then several other critical security flaws have to also have happened. And how far does this thing need to go? Isn't it defeatable if I chop up the keywords into benign ones, store as variables, and then expand them? I guess it stops very low hanging fruit attackers but again, isn't that also only in the situations where there are also low hanging fruit attacks available which can cause far more damage? That's where my confusion is coming from.

There is no exploit... for this specific site.

But the WAF rule is not site-specific.

Almost all of your comment is asking site-specific questions, but that's barking up the wrong tree. The WAF is working under a completely different paradigm.

It especially doesn't know about specific user rules within a specific site! Or file permissions. None of those are in scope for the WAF. The WAF is trying to protect a million sites at once.

> Isn't it defeatable if I chop up the keywords into benign ones, store as variables, and then expand them?

That might work half the time, but not the other half. The filter isn't pointless, it's just being badly and annoyingly applied.

> I asked why setting permissions was not a sufficient solution.

/etc/passwd is readable by design by every user in Linux. And you have it even inside the containers. If you set permissions to "readable by root only" normal programs won't be able to map user names to ids and your application might die

In modern linux this file doesn't contain any passwords, the only thing the attacker can gain by reading it is learning some usernames

I haven't been in the business of writing WAFs, but if I got an assignment of "block every string in the request body that contains /etc/passwd or /etc/hosts, including filenames in multipart forms" – I would strongly debate that with the PMs requesting that. And - probably - debate for some kind of "This website is served by an application developed by people who know what they are doing" checkbox, which would instantly neuter rules like that.

I had a problem recently trying to send LLM-generated text between two web servers under my control, from AWS to Render - I was getting 403s for command injection from Render's Cloudflare protection which is opaque and unconfigurable to users.

The hacky workaround which has been stably working for a while now was to encode the offending request body and decode it on the destination server.

This reminds me of that time I was discussing with friends about something we did in our computer science class that day and I realised writing toString in the Whatsapp client for macOS would crash the application. At the time I didn’t have the skills to understand why so I recorded the bug on my phone to share with friends :)

Just rot13 any request data using javascript before posting, and rot13 it again on the server side. Problem solved. (jk)

This is a common problem with WAFs and, more specifically, Cloudflare's default rulesets. If your platform has content that is remotely technical you'll end up triggering some rules. You end up needing a test suite to confirm your real content doesn't trigger the rules and if it does you need to disable them.

substack also does wonderful things like preserve weird bullet points, lack code block displays, and make it impossible to customize the landing page of your site beyond the 2 formats they give you.

generally think that Substack has done a good thing for its core audience of longform newsletter writer creators who want to be Ben Thompson. however its experience for technical people, for podcasters, for people who want to start multi-channel media brands, and for people who write for reach over revenue (but with optional revenue) has been really poor. (all 4 of these are us with Latent.Space). I've aired all these complaints with them and theyve done nothing, which is their prerogative.

i'd love for "new Substack" to emerge. or "Substack for developers".

Ben Thompson is working on Passport, which seems to be a self-hosted (WordPress-based) Substack: https://stratechery.com/2021/passport/

He gave a talk on it at WordCamp Asia at the start of last year, although I haven’t heard of any progress recently on it.

You're missing the point of Substack:

1. It's a social media platform with a network that is still easy to extract organic growth from.

2. 99% email deliverability without configuring anything. It's whitelisted everywhere.

This isn't a "security vs usability" trade-off as the author implies. This has nothing to do with security at all.

/etc/hosts

See, HN didn't complain. Does this mean I have hacked into the site? No, Substack (or Cloudflare, wherever the problem is) is run by people who have no idea how text input works.

It's more so that Cloudflare has a WAF product that checks a box for security and makes people who's job it is to care about boxes being checked happy.

For example, I worked with a client that had a test suite of about 7000 or so strings that should return a 500 error, including /etc/hosts and other ones such as:

  ../../apache/logs/error.log
  AND%20(SELECT%208203%20FROM%20(SELECT(SLEEP(5)))xGId)
  /../..//../..//../..//../winnt/system32/netstat.exe?-a

We ended up deploying a WAF to block all these requests, even though it didn't improve security in any meaningful way.

> For example, I worked with a client that had a test suite of about 7000 or so strings that should return a 500 error

> We "failed" and were not in compliance as you could make a request containing one of those strings--ignoring that neither Apache, SQL, or Windows were in use.

this causes me pain

Why in the world should those be 500 even? Those all are "40x client fuckup".

I guess someone was told, when compiling those strings, that they should observe this known-good implementation (that actually crashed upon receiving such things) and record whatever it returns, and then mandate it of everyone else from now on.

What is their desired behaviour if not a 404? A 500? a FIN? a RST?

The desired result is a 500 so it's possible to audit.

As much as this is a pain, the alternative can be more painful.

I used to have a client that would forward me an email from their security team every six weeks saying "we found a SQL injection issue with your site, can you look into this and confirm that it's fixed?" and I'd reply back saying "that not possible" and they'd go "ok, we've marked this as a false positive".

Eventually I got bored of having the same conversation over and over, so I asked them to show what they were finding. It turned out their scan would do the following:

  html1 = request("https://example.com/search?query=test")
  html2 = request("https://example.com/search?query=test' or 1=1--")
  if (html1 != html2) 
    sql_injection_vulnerable = true

This is a perfect use case for a WAF, I can stick one in front and then have it return 500s for all these requests and not worry about it any more.

In our case, we didn't have a WAF, but they had a obvious User-Agent, and it turns out that blocking all of their requests passed the scan too :)

This is like banning quotes from your website to 'solve' SQL injection...

"magic quotes" have entered the chat :D

> is run by people who have no idea how text input works

That's a very uncharitable view. It's far more likely that they are simply using some WAF with sane defaults and never caught this. They'll fix it and move on.

with insane defaults FTFY

My thought exactly - this isn't an example of balance between "security vs usability" - this is just wrong behaviour.

It's a text string that is frequently associated with attacks and vulnerabilities. In general you want your WAF to block those things. This is indeed the point of a WAF. Except you also don't want it to get in the way of normal functionality (too much). That is what the security vs usability trade off is.

This particular rule is obviously off. I suspect it wasn't intended to apply to the POST payload of user content. Perhaps just URL parameters.

On a big enough website, users are doing weird stuff all the time and it can be tricky to write rules that stop the traffic you don't want while allowing every oddball legitimate request.

Your auditor wants your WAF to block those things. _You_, at least I, never ever want to have a WAF at all, as they cause much more harm than good and, as a product category, deserve to die.

> Substack's filter is well-intentioned - protecting their platform from potential attacks.

There is sadly no evidence in this article that the supposed filter does protect the platform from potential attacks.

The amount of headaches I've had from WAFs blocking legit stuff is unreal. I just wish the folks turning those rules on had to use them for a week themselves.

Using a WAF is the strongest indicator that someone doesn't know what's happening and where or something underneath is smelly and leaking profusely.

The title would be improved with "Writing the string ...". I first read it as "Writing the file" which was pretty weird.

It's in quotation marks, which I'd say makes it clear enough for most people.

I once helped maintain some PHP software that was effectively a CMS. You'd drop a little PHP snippet into any page (e.g., that you make with Dreamweaver) and it would automatically integrate it with the CMS functionality.

We had unending trouble with mod_security. The worst issue I can remember was that any POST request whose body contained the word "delete" was automatically rejected. That was the full rule. To this day I still can't imagine what the developers were thinking.

Just tried to post a tweet with this article title and link and got a similar error (on desktop twitter.com). Lovely.

Did anyone try reporting this to Substack?

Similar:

Writing `find` as the first word in your search will prevent Firefox from accepting the “return” key is pressed.

Pretty annoying.

I can't reproduce this; is it still the case, or some ancient thing?

I can't reproduce it, either, using FF 137.0.2 (64-bit) on Windows.

Are you sure you don't have a custom search rule configured in Firefox? I just tried this on my local instance and there was no problem.

EDIT: Apparently this is caused by the “findplus” extension. Removed!

So "/etc/h*sts" is not stopped by the filters? Nice to know for the hackers :)

So everyone should start looking for vulnerabilities in the substack site?

If that's their idea of security...

Aaaahh they are trying to prevent a Little Bobby Tables story..

this feels like blocking terms like "null" or "select" just because you failed to properly parameterize your SQL queries.

writing "bcc: someone@email.com" sometimes triggers WAF rules

Ok so: there is a blogging/content publishing engine, which is somewhat of a darling of the startup scene. There is a cloud hosting company with a variety of products, which is an even dearer darling of the startup scene. Something is posted on the blobbing/content publishing engine that clearly reveals that

* The product provided for blogging/content publishing did a shitty job of configuring WAF rules for its use cases (the utility of a "magic WAF that will just solve all your problems" being out of the picture for now) * The WAF product provided by the cloud platform clearly has shitty, overreaching rules doing arbitrary filtering on arbitrary strings. That filtering absolutely can (and will) break unrelated content if the application behind the WAF is developed with a modicum of security-mindedness. You don't `fopen()` a string input (no, I will not be surprised - yes, sometimes you do `fopen()` a string input - when you are using software that is badly written).

So I am wondering:

1. Was this sent to Substack as a bug - they charge money for their platform, and the inability to store $arbitrary_string on a page you pay for, as a user, is actually a malfunction and disfunction"? It might not be the case "it got once enshittified by a CIO who mandated a WAF of some description to tick a box", it might be the case "we grabbed a WAF from our cloud vendor and haven't reviewed the rules because we had no time". I don't think it would be very difficult for me, as an owner/manager at the blogging platform, to realise that enabling a rule filtering "anything that resembles a Unix system file path or a SQL query" is absolutely stupid for a blogging platform - and go and turn it the hell off at the first user complaint.

2. Similarly - does the cloud vendor know that their WAF refuses requests with such strings in them, and do they have a checkbox for "Kill requests which have any character an Average Joe does not type more frequently than once a week"? There should be a setting for that, and - thinking about the cloud vendor in question - I can't imagine the skill level there would be so low as to not have a config option to turn it off.

So - yes, that's a case of "we enabled a WAF for some compliance/external reasons/big customer who wants a 'my vendor uses a WAF' on their checklist", but also the case of "we enabled a WAF but it's either buggy or we haven't bothered to configure it properly".

To me it feels like this would be 2 emails first ("look, your thing <X> that I pay you money for clearly and blatantly does <shitty thing>, either let me turn it off or turn it off yourself or review it please") - and a blog post about it second.

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You figured all that out just because the headers indicate the site passed through Cloudflare at one point? That's quite a leap!

If Cloudflare had a default rule that made it impossible to write that string on any site with their WAF, wouldn't this be a lot more widespread? Much more likely someone entered a bad rule into Cloudflare, or Cloudflare isn't involved in that rule at all.

Huh, a bit like "adult-content" filters that would censor Scunthorpe or Wikipedia articles about genitals, maybe Cloudflare saw a market to sell protection for donkeys who can't protect their webapps from getting request-injected.

I think Cloudflare WAF is a good product compared to other WAFs - by definition a WAF is intended to layer on validation that properly built applications should be doing, so it's sort of expected that it would reject valid potentially harmful content.

I think you can fairly criticise WAF products and the people who advocate for them (and created the need for them) but I don't think the CF team responsible can really be singled out.

Unfortunately this is probably a case where the market demands stupidity. The quality engineers don't have a say over market forces.

Who knows how many attacks such a "stupid" thing blocks every month?

These WAF features are older than LLMs & vibe coding.

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Worth noting that people here are assuming that the author's assumption is correct, that his writing /etc/hosts is causing the 403, and that this is either a consequence of security filtering, or that this combination of characters at all that's causing the failure. The only evidence he has, is he gets back a 403 forbidden to an API request when he writes certain content. There's a thousand different things that could be triggering that 403.

It's not likely to be a WAF or content scanner, because the HTTP request is using PUT (which browser forms don't use) and it's uploading the content as a JSON content-type in a JSON document. The WAF would have to specifically look for PUTs, open up the JSON document, parse it, find the sub-string in a valid string, and reject it. OR it would have to filter raw characters regardless of the HTTP operation.

Neither of those seem likely. WAFs are designed to filter on specific kinds of requests, content, and methods. A valid string in a valid JSON document uploaded by JavaScript using a JSON content-type is not an attack vector. And this problem is definitely not path traversal protection, because that is only triggered when the string is in the URL, not some random part of the content body.

It sure looks like the author did his due diligence; he has a chart of all the different phrases in the payload which triggered the 403 and they all corresponded to paths to common UNIX system configuration files.

Nobody could prove that's exactly what's happening without seeing Cloudflare's internal WAF rules, but can you think of any other reasonable explanation? The endpoint is rejecting a PUT who's payload contains exactly /etc/hosts, /etc/passwd, or /etc/ssh/sshd_config, but NOT /etc/password, /etc/ssh, or /etc/h0sts. What else could it be?

Yeah, the author clearly put the work in to demonstrate what's happening here.

If you change a single string in the HTTP payload and it works, what other explanation makes sense besides a text scanner somewhere along the path to deploying the content?

See https://developers.cloudflare.com/waf/change-log/2025-04-22/ rule 100741.

It references this CVE https://github.com/tuo4n8/CVE-2023-22047 which allows the reading of system files. The example given shows them reading /etc/passwd

You're being downvoted because WAFs work exactly like this, and it's intentional and their vendors think this is a good thing. A WAF vendor would say that a WAF parsing JSON makes it weaker.

They're being downvoted because they're saying the author is incorrect when the author is actually correct.

It's frightening that so many people are convinced the author is correct, when the author never proved they were correct.

The author just collected a bunch of correlations and then decided what the cause was. I've been doing this kind of work for many, many years. Just because it looks like it's caused by one thing, doesn't mean it is.

Correlation is not causation. That's not just a pithy quip, there's a reason why it's important to actually find causation.

Having had three opportunities in my life to diagnose this exact problem and then successfully resolve it by turning off the WAF rule (see my top level comment) - I don't know you or your work history, but trust me, the author is much closer to the truth here than you are.

edit: Also, someone commented here "it was an irrelevant cf WAF rule, we disabled it". Assuming honesty, seems to confirm that the author was indeed right.

It's more like I saw a big ball fall down and make a hole in the floor and concluded it must be heavy.