A flaw was found in the QEMU Guest Agent (qga). A local unprivileged user can exploit a vulnerability in the guest-ssh-add-authorized-keys command handler by manipulating symbolic links. This can occur either through a deterministic directory-symlink bypass or a Time-of-Check to Time-of-Use (TOCTOU) file-symlink race. Successful exploitation allows the attacker to gain ownership of arbitrary root-owned files or directories, leading to root access. This vulnerability requires an external management layer (e.g., libvirt) to trigger the affected code path.
If the guest-ssh-add-authorized-keys command is not required, it can be disabled by adding it to the qemu-guest-agent block list (qemu-ga --block-rpcs). This prevents the vulnerable code path from being reached while preserving all other guest-agent functionality.