The integrity check feature in OpenPGP, when handling a message that was encrypted using cipher feedback (CFB) mode, allows remote attackers to recover part of the plaintext via a chosen-ciphertext attack when the first 2 bytes of a message block are known, and an oracle or other mechanism is available to determine whether an integrity check failed.
http://www.securityfocus.com/bid/12529
http://www.kb.cert.org/vuls/id/303094
http://www.gentoo.org/security/en/glsa/glsa-200503-29.xml
http://securitytracker.com/id?1013166