The key selection dialogue in Enigmail before 0.92.1 can incorrectly select a key with a user ID that does not have additional information, which allows parties with that key to decrypt the message.
http://www.vupen.com/english/advisories/2005/2158
http://www.securityfocus.com/bid/15155
http://www.novell.com/linux/security/advisories/2005_28_sr.html
http://www.mandriva.com/security/advisories?name=MDKSA-2005:226
http://www.kb.cert.org/vuls/id/805121