go-git: Crafted repositories may modify main and submodule .git directories

Vulnerability

A path validation issue exists in go-git, a pure-Go Git implementation [1]. The flaw allows crafted repository data to bypass checks that were introduced in upstream Git years ago, leading to filesystem writes outside the intended checkout target, including the repository's .git directory. Versions prior to v5 are likely affected [2][3]. Some attack vectors are platform-specific: certain payloads affect only Windows users, others only macOS users, and some apply across all supported platforms [2][3].

Exploitation

Exploitation requires a maliciously crafted repository payload [2][3]. An attacker must convince the victim to clone or interact with a repository they control (e.g., from an untrusted Git server). No additional authentication is needed beyond normal clone or checkout operations. The vulnerability is triggered when go-git processes path traversal sequences or specially crafted filenames during checkout. Using non-descendant go-billy filesystem instances or different filesystem types for the Storer and Worktree may provide some isolation, but this does not apply when submodules are present — submodule .git directories may still be materialized in the worktree context [2][3].

Impact

Successful exploitation allows an attacker to write files outside the intended checkout directory, including into the repository's own .git directory [2][3]. This can lead to arbitrary file modification, potentially enabling subsequent code execution (e.g., by altering Git hooks in .git/hooks/). The impact is limited to the scope of the application's filesystem permissions, and no privilege escalation beyond the user running go-git is implied. The vulnerability affects confidentiality, integrity, and availability depending on the attacker's goals.

Mitigation

Users should upgrade to a patched version of go-git [2][3]. Versions prior to v5 are likely affected; upgrading to a supported go-git version (v5 or later) is recommended. No specific patch version or release date for v5 is given in the references. As a partial workaround, using non-descendant go-billy filesystem instances for Storer and Worktree (e.g., memfs for .git storage and osfs for worktree) may reduce risk, but this does not protect against submodule-based attacks [2][3]. Users should also exercise caution when interacting with repositories from untrusted sources [2][3].