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GitPython untrusted search path on Windows systems leading to arbitrary code execution
When resolving a program, Python/Windows look for the current working directory, and after that the PATH environment (see big warning in https://docs.python.org/3/library/subprocess.html#popen-constructor). GitPython defaults to use the git command, if a user runs GitPython from a repo has a git.exe or git executable, that program will be run instead of the one in the user's PATH.
Details
This is more of a problem on how Python interacts with Windows systems, Linux and any other OS aren't affected by this. But probably people using GitPython usually run it from the CWD of a repo.
And there are other commands executed that should probably be aware of this problem.
PoC
On a Windows system, create a git.exe or git executable in any directory, and import or run GitPython from that directory
python -c "import git"
The git executable from the current directory will be run.
Impact
An attacker can trick a user to download a repository with a malicious git executable, if the user runs/imports GitPython from that directory, it allows the attacker to run any arbitrary commands.
Possible solutions
Default to an absolute path for the git program on Windows, like C:\\Program Files\\Git\\cmd\\git.EXE (default git path installation).
Require users to set the GIT_PYTHON_GIT_EXECUTABLE environment variable on Windows systems.
Make this problem prominent in the documentation and advise users to never run GitPython from an untrusted repo, or set the GIT_PYTHON_GIT_EXECUTABLE env var to an absolute path.
Resolve the executable manually by only looking into the PATH environment variable (suggested by @Byron)
Note
This vulnerability was reported via email, and it was decided to publish it here and make it public, so the community is aware of it, and a fix can be provided.
stsewd Reporter
MicaelJarniac Analyst
Summary
When resolving a program, Python/Windows look for the current working directory, and after that the PATH environment (see big warning in https://docs.python.org/3/library/subprocess.html#popen-constructor). GitPython defaults to use the
gitcommand, if a user runs GitPython from a repo has agit.exeorgitexecutable, that program will be run instead of the one in the user'sPATH.Details
This is more of a problem on how Python interacts with Windows systems, Linux and any other OS aren't affected by this. But probably people using GitPython usually run it from the CWD of a repo.
The execution of the
gitcommand happens inhttps://github.com/gitpython-developers/GitPython/blob/1c8310d7cae144f74a671cbe17e51f63a830adbf/git/cmd.py#L277
https://github.com/gitpython-developers/GitPython/blob/1c8310d7cae144f74a671cbe17e51f63a830adbf/git/cmd.py#L983-L996
And there are other commands executed that should probably be aware of this problem.
PoC
On a Windows system, create a
git.exeorgitexecutable in any directory, and import or run GitPython from that directoryThe git executable from the current directory will be run.
Impact
An attacker can trick a user to download a repository with a malicious
gitexecutable, if the user runs/imports GitPython from that directory, it allows the attacker to run any arbitrary commands.Possible solutions
C:\\Program Files\\Git\\cmd\\git.EXE(default git path installation).GIT_PYTHON_GIT_EXECUTABLEenvironment variable on Windows systems.GIT_PYTHON_GIT_EXECUTABLEenv var to an absolute path.PATHenvironment variable (suggested by @Byron)Note
This vulnerability was reported via email, and it was decided to publish it here and make it public, so the community is aware of it, and a fix can be provided.
References