go-git missing validation decoding Index v4 files leads to panic

Impact

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.

An attacker able to supply a crafted .git/index file can cause applications using go-git to panic while reading the index. If the application does not recover from panics, this results in process termination, leading to a denial-of-service (DoS) condition.

Exploitation requires the ability to modify or inject a Git index file within the local repository in disk. This typically implies write access to the .git directory.

Patches

Users should upgrade to v5.17.1, or the latest v6 pseudo-version, in order to mitigate this vulnerability.

Credit

go-git maintainers thank @kq5y for finding and reporting this issue privately to the go-git project.