Qemu-kvm: qemu-guest-agent: local privilege escalation via symlink attack in guest-ssh-add-authorized-keys

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.