go-git's improper parsing of specially crafted objects may lead to inconsistent interpretation compared to upstream Git

Impact

go-git may parse malformed Git objects in a way that differs from upstream Git. When commit or tag objects contain ambiguous or malformed headers, go-git’s decoded representation may expose values differently from how Git itself would interpret or reject the same object.

Additionally, go-git’s commit signing and verification logic operates over commit data reconstructed from go-git’s parsed representation rather than the original raw object bytes. As a result, go-git may sign or verify a commit payload that is not byte-for-byte equivalent to the object stored in the repository.

This can cause a signature to appear valid for a commit whose displayed or effective metadata differs from the object that was intended to be signed.

Patches

Users should upgrade to a patched version in order to mitigate this vulnerability. Versions prior to v5 are likely to be affected, users are recommended to upgrade to a supported go-git version.

Credit

Thanks to @bugbunny-research (https://bugbunny.ai/) for reporting this to sigstore/gitsign, and to @wlynch, @patzielinski and @adityasaky for coordinating the disclosure with the go-git project. :bow: :1st_place_medal:

Thanks to @wayphinder for reporting this to the go-git project. :bow: