The match_component function in smtp-tls.c in libESMTP 1.0.3.r1, and possibly other versions including 1.0.4, treats two strings as equal if one is a substring of the other, which allows remote attackers to spoof trusted certificates via a crafted subjectAltName.
http://www.vupen.com/english/advisories/2010/1107
http://www.openwall.com/lists/oss-security/2010/03/09/3
http://www.openwall.com/lists/oss-security/2010/03/03/6
http://lists.opensuse.org/opensuse-security-announce/2010-05/msg00001.html