Breaking Git with a carriage return and cloning RCE

> The result of all this, is when a submodule clone is performed, it might read one location from path = ..., but write out a different path that doesn’t end with the ^M.

How does this achieve “remote code execution” as the article states? How serious is it from a security perspective?

> I'm not sharing a PoC yet, but it is an almost trivial modification of an exploit for CVE-2024-32002. There is also a test in the commit fixing it that should give large hints.

EDIT: from the CVE-2024-32002

> Repositories with submodules can be crafted in a way that exploits a bug in Git whereby it can be fooled into writing files not into the submodule's worktree but into a .git/ directory. This allows writing a hook that will be executed while the clone operation is still running, giving the user no opportunity to inspect the code that is being executed.

So a repository can contain a malicious git hook. Normally git hooks aren’t installed by ‘git clone’, but this exploit allows one to, and a git hook can run during the clone operation.

In this case, there is more than enough information given to make an exploit trivial for anyone actually investigating the issue. I don’t see a reason to distribute PoC exploit code here, it’s fairly clear what the problem is as well as at least one possible RCE implementation.

A well-written article should still have spelled out what armchairhacker did. The article spent many paragraphs working through what seemed to me like a very obvious chain of reasoning that didn't need so much hand-holding, and then left me completely bewildered at the end with the last step. And even with the explanation, I'm still not sure why writing the files to a different path allows the hook to be written. (Surely Git knows that it's still in the middle of a recursive clone operation and that it therefore shouldn't accept any hooks?)

Git does "know" that – but it doesn't know it's writing a hook.