gnupg -- AEAD key import overflow

Importing an OpenPGP key having a preference list for AEAD algorithms will lead to an array overflow and thus often to a crash or other undefined behaviour.

Importing an arbitrary key can often easily be triggered by an attacker and thus triggering this bug. Exploiting the bug aside from crashes is not trivial but likely possible for a dedicated attacker. The major hurdle for an attacker is that only every second byte is under their control with every first byte having a fixed value of 0x04.