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I used o3 to find a remote zeroday in the Linux SMB implementation

sean.heelan.io

31–40 of 232 posts

Re: I used o3 to find a remote zeroday in the Linux SMB implementation

#31
> With o3 you get something that feels like a human-written bug report, condensed to just present the findings, whereas with Sonnet 3.7 you get something like a stream of thought, or a work log.

This is likely because the author didn't give Claude a scratchpad or space to think, essentially forcing it to mix its thoughts with its report. I'd be interested to see if using the official thinking mechanism gives it enough space to get differing results.

Re: I used o3 to find a remote zeroday in the Linux SMB implementation

#32

My understanding is that ksmbd is a kernel-space SMB server "developed as a lightweight, high-performance alternative" to the traditional (user-space) Samba server... Q1: Who is using ksmbd in production? Q2: Why?

1. People that were using the in-kernel SMB server in Solaris or Windows. 2. Samba performance sucks (by comparison) which is why people still regularly deploy Windows for file sharing in 2025. Anybody know if this supports native Windows-style ACLs for file permissions? That is the last remaining reason to still run Solaris but I think it relies on ZFS to do so. Samba's reliance on Unix UID/GID and the syncing as pa…

> Samba's reliance on Unix UID/GID and the syncing as part of its security model is still stuck in the 1970s unfortunately.

Sigh. This is why we can't have nice things

Like yeah having smb in kernel is faster but honestly it's not fundamentally faster. But it seems the will to make samba better isn't there

Re: I used o3 to find a remote zeroday in the Linux SMB implementation

#33
A small thing, but I found the author's project-organization practices useful – creating individual .prompt files for system prompt, background information, and auxiliary instructions [1], and then running it through `llm`.

It reveals how good LLM use, like any other engineering tool, requires good engineering thinking – methodical, and oriented around thoughtful specifications that balance design constraints – for best results.

[1] https://github.com/SeanHeelan/o3_finds_cve-2025-37899

Re: I used o3 to find a remote zeroday in the Linux SMB implementation

#35
post #19

Meanwhile, as a maintainer, I've been reviewing more than a dozen false positives slop CVEs in my library and not a single one found an actual issue. This article's is probably going to make my situation worse.

Maybe, but the author is an experienced vulnerability analyst. Obviously if you get a lot of people who have no experience with this you may get a lot of sloppy, false reports.

But this poster actually understands the AI output and is able to find real issues (in this case, use-after-free). From the article:

> Before I get into the technical details, the main takeaway from this post is this: with o3 LLMs have made a leap forward in their ability to reason about code, and if you work in vulnerability research you should start paying close attention. If you’re an expert-level vulnerability researcher or exploit developer the machines aren’t about to replace you. In fact, it is quite the opposite: they are now at a stage where they can make you significantly more efficient and effective.

Re: I used o3 to find a remote zeroday in the Linux SMB implementation

#36
post #6

Earlier quoted context omitted.

He did do exactly what you say – except right after that, while reviewing the outputs, he found that it had also discovered a different 0day.

Now the question is whether spending same time to analyze that bit of code instead of throwing automated intern at it would be time spent better

[deleted]

Re: I used o3 to find a remote zeroday in the Linux SMB implementation

#38

The most interesting and significant bit of this article for me was that the author ran this search for vulnerabilities 100 times for each of the models. That's significantly more computation than I've historically been willing to expend on most of the problems that I try with large language models, but maybe I should let the models go brrrrr!

A lot of money is all you need~

A lot of burned coal, is what.

The "don't blame the victim" trope is valid in many contexts. This one application might be "hackers are attacking vital infrastructure, so we need to fund vulnerabilities first". And hackers use AI now, likely hacked into and for free, to discover vulnerabilities. So we must use AI!

Therefore, the hackers are contributing to global warming. We, dear reader, are innocent.

Re: I used o3 to find a remote zeroday in the Linux SMB implementation

#40

My understanding is that ksmbd is a kernel-space SMB server "developed as a lightweight, high-performance alternative" to the traditional (user-space) Samba server... Q1: Who is using ksmbd in production? Q2: Why?

Licensing. Samba is GPLv3, Linux is only GPLv2.
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