Impact

A specially crafted repository that contains symbolic links as well as files using a clean/smudge filter such as Git LFS, may cause just-checked out script to be executed while cloning onto a case-insensitive file system such as NTFS, HFS+ or APFS (i.e. the default file systems on Windows and macOS).

Note that clean/smudge filters have to be configured for that. Git for Windows configures Git LFS by default, and is therefore vulnerable.

Patches

The problem has been patched in the versions published on Tuesday, March 9th, 2021.

Workarounds

If symbolic link support is disabled in Git (e.g. via git config --global core.symlinks false), the described attack won't work.

Likewise, if no clean/smudge filters such as Git LFS are configured globally (i.e. before cloning), the attack is foiled.

As always, it is best to avoid cloning repositories from untrusted sources.

Credits

Credit for finding and fixing the vulnerability goes to Matheus Tavares and Johannes Schindelin.

References

• https://lore.kernel.org/git/xmqqim6019yd.fsf@gitster.c.googlers.com/
• https://git-scm.com/docs/git-config#Documentation/git-config.txt-coresymlinks
• https://git-scm.com/docs/gitattributes#_filter
• 684dd4c
• https://github.com/git-for-windows/git/releases/tag/v2.30.2.windows.1

For more information

If you have any questions or comments about this advisory:

• For public questions, contact the Git mailing list (details at https://git-scm.com/community)
• To disclose further vulnerabilities privately, contact the Git-security list by emailing git-security@googlegroups.com