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 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.
The execution of the git command happens in
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git_exec_name = "git" # default that should work on linux and windows |
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proc = Popen( |
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command, |
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env=env, |
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cwd=cwd, |
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bufsize=-1, |
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stdin=istream or DEVNULL, |
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stderr=PIPE, |
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stdout=stdout_sink, |
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shell=shell is not None and shell or self.USE_SHELL, |
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close_fds=is_posix, # unsupported on windows |
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universal_newlines=universal_newlines, |
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creationflags=PROC_CREATIONFLAGS, |
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**subprocess_kwargs, |
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) |
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
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.
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 inGitPython/git/cmd.py
Line 277 in 1c8310d
GitPython/git/cmd.py
Lines 983 to 996 in 1c8310d
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.