go-git improperly verifies data integrity values for .idx and .pack files

Impact

A vulnerability was discovered in go-git whereby data integrity values for .pack and .idx files were not properly verified. This resulted in go-git potentially consuming corrupted files, which would likely result in unexpected errors such as object not found.

For context, clients fetch packfiles from upstream Git servers. Those files contain a checksum of their contents, so that clients can perform integrity checks before consuming it. The pack indexes (.idx) are generated locally by go-git, or the git cli, when new .pack files are received and processed. The integrity checks for both files were not being verified correctly.

Note that the lack of verification of the packfile checksum has no impact on the trust relationship between the client and server, which is enforced based on the protocol being used (e.g. TLS in the case of https:// or known hosts for ssh://). In other words, the packfile checksum verification does not provide any security benefits when connecting to a malicious or compromised Git server.

Patches

Users should upgrade to v5.16.5, or the latest v6 pseudo-version, in order to mitigate this vulnerability.

Workarounds

In case updating to a fixed version of go-git is not possible, users can run git fsck from the git cli to check for data corruption on a given repository.

Credit

Thanks @N0zoM1z0 for finding and reporting this issue privately to the go-git project.