Claude Wrote a Full FreeBSD Remote Kernel RCE with Root Shell (CVE-2026-4747)

https://github.com/califio/publications/blob/main/MADBugs/CVE-2026-4747/write-up.md

publications/MADBugs/CVE-2026-4747/write-up.md at main · califio/publications

Publications from Calif. Contribute to califio/publications development by creating an account on GitHub.

GitHub
I'm just gonna assume it was asked to fix some bug and it wrote exploit instead

Key point is that Claude did not find the bug it exploits. It was given the CVE writeup[1] and was asked to write a program that could exploit the bug.

That said, given how things are I wouldn't be surprised if you could let Claude or similar have a go at the source code of the kernel or core services, armed with some VMs for the try-fail iteration, and get it pumping out CVEs.

If not now, then surely not in a too distant future.

[1]: https://www.freebsd.org/security/advisories/FreeBSD-SA-26:08...

> Credits: Nicholas Carlini using Claude, Anthropic

Claude was used to find the bug in the first place though. That CVE write-up happened because of Claude, so while there are some very talented humans in the loop, Claude is quite involved with the whole process.

> Claude was used to find the bug in the first place though. That CVE write-up happened because of Claude

Do you have a link to that? A rather important piece of context.

Wasn't trying to downplay this submission the way, the main point still stands:

But finding a bug and exploiting it are very different things. Exploit development requires understanding OS internals, crafting ROP chains, managing memory layouts, debugging crashes, and adapting when things go wrong. This has long been considered the frontier that only humans can cross.

Each new AI capability is usually met with “AI can do Y, but only humans can do X.” Well, for X = exploit development, that line just moved.

> have a go at the source code of the kernel or core services, armed with some VMs for the try-fail iteration, and get it pumping out CVEs.

FreeBSD kernel is written in C right?

AI bots will trivially find CVEs.

The Morris worm lesson is yet to be taken seriously.
We’re here right now looking at a CVE. That has to count as progress?
Appreciate the full prompt history
Well, it ends with "can you give me back all the prompts i entered in this session", so it may be partially the actual prompt history and partially hallucination.

The talk "Black-Hat LLMs" just came out a few days ago:

https://www.youtube.com/watch?v=1sd26pWhfmg

Looks like LLMs are getting good at finding and exploiting these.

Nicholas Carlini - Black-hat LLMs | [un]prompted 2026

Nicholas Carlini, Research Scientist, Anthropic, speaks at [un]prompted 2026 on: Black-hat LLMs.Large language models are now capable of automating attacks t...

YouTube

Everybody is acts so surprised as if nobody (around here of all places!) read the sama tweet in which he was hiring the Head of Preparedness... in December.

https://xcancel.com/sama/status/2004939524216910323

Sam Altman (@sama)

We are hiring a Head of Preparedness. This is a critical role at an important time; models are improving quickly and are now capable of many great things, but they are also starting to present some real challenges. The potential impact of models on mental health was something we saw a preview of in 2025; we are just now seeing models get so good at computer security they are beginning to find critical vulnerabilities. We have a strong foundation of measuring growing capabilities, but we are entering a world where we need more nuanced understanding and measurement of how those capabilities could be abused, and how we can limit those downsides both in our products and in the world, in a way that lets us all enjoy the tremendous benefits. These questions are hard and there is little precedent; a lot of ideas that sound good have some real edge cases. If you want to help the world figure out how to enable cybersecurity defenders with cutting edge capabilities while ensuring attackers can't use them for harm, ideally by making all systems more secure, and similarly for how we release biological capabilities and even gain confidence in the safety of running systems that can self-improve, please consider applying. This will be a stressful job and you'll jump into the deep end pretty much immediately. https://openai.com/careers/head-of-preparedness-san-francisco/

Nitter

> It's worth noting that FreeBSD made this easier than it would be on a modern Linux kernel: FreeBSD 14.x has no KASLR (kernel addresses are fixed and predictable) and no stack canaries for integer arrays (the overflowed buffer is int32_t[]).

What about FreeBSD 15.x then? I didn't see anything in the release notes or the mitigations(7) man page about KASLR. Is it being worked on?

NetBSD apparently has it: https://wiki.netbsd.org/security/kaslr/

Using KASLR