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Claude Code Found a Linux Vulnerability Hidden for 23 Years

mtlynch.io

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Re: Claude Code Found a Linux Vulnerability Hidden for 23 Years

#151
post #49

Earlier quoted context omitted.

Those aren't false positives; they're results he hasn't yet inspected. I wrote a longer reply here: https://news.ycombinator.com/item?id=47638062

> Those aren't false positives; they're results he hasn't yet inspected. It's not a XOR

Yes it is. They're not not false positives until they're reported and consume maintainer time.

Re: Claude Code Found a Linux Vulnerability Hidden for 23 Years

#152

Earlier quoted context omitted.

This is where the Codex and Claude Code Pro/Max plans are excellent. I rarely run into the limits of Codex. If I do, I wait and come back and have it resume once the window has expired.

Claude and Codex pro/max subs aren't supposed to be used for commercial/enterprise development so its not really an option for execs in enterprise. They need to take into account API costs. At my F500 company execs are very wary of the costs of most of these tools and its always top of mind. We have dashboards and gather tons of internal metrics on which tools devs are using and how much they are costing.

No, I think that’s wrong. They aren’t supposed to be put behind a service, but they can certainly be used to write professional products/ products for the enterprise.

Re: Claude Code Found a Linux Vulnerability Hidden for 23 Years

#153
post #57

Pasting a big batch of new code and asking Claude "what have I forgotten? Where are the bugs?" is a very persuasive on-ramp for developers new to AI. It spots threading & distributed system bugs that would have taken hours to uncover before, and where there isn't any other easy tooling. I bet there's loads of cryptocurrency implementations being pored over right now - actual money on the table.

[dead]

Re: Claude Code Found a Linux Vulnerability Hidden for 23 Years

#154

This isn't surprising. What is not mentioned is that Claude Code also found one thousand false positive bugs, which developers spent three months to rule out.

That's not what is happening right now. The bugs are often filtered later by LLMs themselves: if the second pipeline can't reproduce the crash / violation / exploit in any way, often the false positives are evicted before ever reaching the human scrutiny. Checking if a real vulnerability can be triggered is a trivial task compared to finding one, so this second pipeline has an almost 100% success rate from the POV: i…

> Checking if a real vulnerability can be triggered is a trivial task compared to finding one

Have you ever tried to write PoC for any CVE?

This statement is wrong. Sometimes bug may exist but be impossible to trigger/exploit. So it is not trivial at all.

Re: Claude Code Found a Linux Vulnerability Hidden for 23 Years

#156

This isn't surprising. What is not mentioned is that Claude Code also found one thousand false positive bugs, which developers spent three months to rule out.

Static/Dynamic analysis tools find vulnerabilities all the time. Almost all projects of a certain size have a large backlog of known issues from these boring scanners. The issue is sorting through them all and triaging them. There's too many issues to fix and figuring out which are exploitable and actually damaging, given mitigations, is time consuming. Am i impressed claude found an old bug? Sort of.. everytime a ne…

Static analyzers find large numbers of hypothetical bugs, of which only a small subset are actionable, and the work to resolve which are actionable and which are e.g. "a memcpy into an 8 byte buffer whose input was previously clamped to 8 bytes or less" is so high that analyzers have little impact at scale. I don't know off the top of my head many vulnerability researchers who take pure static analysis tools seriously.

Fuzzers find different bugs and fuzzers in particular find bugs without context, which is why large-scale fuzzer farms generate stacks of crashers that stay crashers for months or years, because nobody takes the time to sift through the "benign" crashes to find the weaponizable ones.

LLM agents function differently than either method. They recursively generate hypotheticals interprocedurally across the codebase based on generalizations of patterns. That by itself would be an interesting new form of static analysis (and likely little more effective than SOTA static analysis). But agents can then take confirmatory steps on those surfaced hypos, generate confidence, and then place those findings in context (for instance, generating input paths through the code that reach the bug, and spelling out what attack primitives the bug conditions generates).

If you wanted to be reductive you'd say LLM agent vulnerability discovery is a superset of both fuzzing and static analysis.

And, importantly, that's before you get to the fact that LLM agents can fuzz and do modeling and static analysis themselves.

Re: Claude Code Found a Linux Vulnerability Hidden for 23 Years

#157
post #147

Earlier quoted context omitted.

Everything changed in the past 6 months and coding LLMs went from being OK-ish to insanely good. People also got better at using them. Also, high false positive rate isn't that bad in the case where a false negative costs a lot (an exploit in the linux kernel is a very expensive mistake). And, in going through the false positives and eliminating them, those results will ideally get folded back into the training set f…

> Everything changed in the past 6 months and coding LLMs went from being OK-ish to insanely good. People also got better at using them. I hear this literally every 6 months :)

It hasn't been true forever, but it has been true over the last 18 months or so.

Re: Claude Code Found a Linux Vulnerability Hidden for 23 Years

#158
post #34

This isn't surprising. What is not mentioned is that Claude Code also found one thousand false positive bugs, which developers spent three months to rule out.

Couldn't you just make it write a PoC?

Yes, you can. I strongly encourage people skeptical about this, and who know at a high-level how this kind of exploitation works, to just try it. Have Claude or Codex (they have different strengths at this kind of work) set up a testing harness with Firecracker or QEMU, and then work through having it build an exploit.

Re: Claude Code Found a Linux Vulnerability Hidden for 23 Years

#159
post #154

Earlier quoted context omitted.

That's not what is happening right now. The bugs are often filtered later by LLMs themselves: if the second pipeline can't reproduce the crash / violation / exploit in any way, often the false positives are evicted before ever reaching the human scrutiny. Checking if a real vulnerability can be triggered is a trivial task compared to finding one, so this second pipeline has an almost 100% success rate from the POV: i…

> Checking if a real vulnerability can be triggered is a trivial task compared to finding one Have you ever tried to write PoC for any CVE? This statement is wrong. Sometimes bug may exist but be impossible to trigger/exploit. So it is not trivial at all.

I'm not GP, but I've written multiple PoCs for vulns. I agree with GP. Finding a vuln is often very hard. Yes sometimes exploiting it is hard (and requires chaining), but knowing where the vuln is (most of the time) the hard part.

Re: Claude Code Found a Linux Vulnerability Hidden for 23 Years

#160

Not "hidden", but probably more like "no one bothered to look". declares a 1024-byte owner ID, which is an unusually long but legal value for the owner ID. When I'm designing protocols or writing code with variable-length elements, "what is the valid range of lengths?" is always at the front of my mind. it uses a memory buffer that’s only 112 bytes. The denial message includes the owner ID, which can be up to 1024 by…

"No one bothered to look" is how most vulnerabilities work. Systems development produces code artifacts with compounding complexity; it is extraordinarily difficult to keep up with it manually, as you know. A solution to that problem is big news.

Static analyzers will find all possible copies of unbounded data into smaller buffers (especially when the size of the target buffer is easily deduced). It will then report them whether or not every path to that code clamps the input. Which is why this approach doesn't work well in the Linux kernel in 2026.

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