The signature verification routine in the Airmail GPG-PGP Plugin, versions 1.0 (9) and earlier, does not verify the status of the signature at all, which allows remote attackers to spoof arbitrary email signatures by crafting a signed email with an invalid signature. Also, it does not verify the validity of the signing key, which allows remote attackers to spoof arbitrary email signatures by crafting a key with a fake user ID (email address) and injecting it into the user's keyring.