Headline
CVE-2022-39253: Local clone optimization dereferences symbolic links by default
Git is an open source, scalable, distributed revision control system. Versions prior to 2.30.6, 2.31.5, 2.32.4, 2.33.5, 2.34.5, 2.35.5, 2.36.3, and 2.37.4 are subject to exposure of sensitive information to a malicious actor. When performing a local clone (where the source and target of the clone are on the same volume), Git copies the contents of the source’s $GIT_DIR/objects directory into the destination by either creating hardlinks to the source contents, or copying them (if hardlinks are disabled via --no-hardlinks). A malicious actor could convince a victim to clone a repository with a symbolic link pointing at sensitive information on the victim’s machine. This can be done either by having the victim clone a malicious repository on the same machine, or having them clone a malicious repository embedded as a bare repository via a submodule from any source, provided they clone with the --recurse-submodules option. Git does not create symbolic links in the $GIT_DIR/objects directory. The problem has been patched in the versions published on 2022-10-18, and backported to v2.30.x. Potential workarounds: Avoid cloning untrusted repositories using the --local optimization when on a shared machine, either by passing the --no-local option to git clone or cloning from a URL that uses the file:// scheme. Alternatively, avoid cloning repositories from untrusted sources with --recurse-submodules or run git config --global protocol.file.allow user.
Impact
When performing a local clone (where the source and target of the clone are on the same volume), Git copies the contents of the source’s $GIT_DIR/objects directory into the destination by either creating hardlinks to the source contents, or copying them (if hardlinks are disabled via --no-hardlinks).
Prior to the patched versions of Git published today, Git’s implementation of its local clone behavior caused it to create hardlinks (or copies) of the dereferenced target of any symbolic links present in the source repository’s $GIT_DIR/objects directory.
A malicious actor could convince a victim to clone a repository with a symbolic link pointing at sensitive information on the victim’s machine. This can be done either by having the victim clone a malicious repository on the same machine, or having them clone a malicious repository embedded as a bare repository via a submodule from any source, provided they clone with the --recurse-submodules option.
Git does not create symbolic links in the $GIT_DIR/objects directory.
Patches
The problem has been patched in the versions published on 2022-10-18, going back to v2.30.x.
Workarounds
The most complete workaround is upgrading to the most recent patched version published.
If doing so is impractical, then there are a couple of short-term workarounds.
- Avoid cloning untrusted repositories using the --local optimization when on a shared machine, by passing the --no-local option to git clone or cloning from a URL that uses the file:// scheme.
- Avoid cloning repositories from untrusted sources with --recurse-submodules. Or, run git config --global protocol.file.allow user.
Credit
Credit for finding the vulnerability goes to Cory Snider of Mirantis.
Wenxiang Qian of Tencent Blade Team reported the symlink copy vulnerability in the docker build command. Bjorn Neergaard of Mirantis discovered that Podman is also vulnerable.
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