go-git: Missing validation decoding Index v4 files leads to panic

go-git is an extensible git implementation library written in pure Go. Prior to version 5.17.1, go-git’s index decoder for format version 4 fails to validate the path name prefix length before applying it to the previously decoded path name. A maliciously crafted index file can trigger an out-of-bounds slice operation, resulting in a runtime panic during normal index parsing. This issue only affects Git index format version 4. Earlier formats (go-git supports only v2 and v3) are not vulnerable to this issue. This issue has been patched in version 5.17.1.