GHSA-389r-gv7p-r3rp

### 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: