Privilege escalation via incomplete repository ownership checks

Local privilege escalation in affected Git releases allows local users to execute arbitrary code through an attacker-created repository. The ensure_valid_ownership function in setup.c verifies only the worktree owner, not the .git directory or gitfile, allowing an attacker-owned repository inside a victim-owned shared directory to pass the safe.directory check. Exploitation requires a higher-privileged user to invoke Git from that shared directory, after which repository configuration such as core.fsmonitor executes attacker-controlled commands with that user's privileges.