Mutt 1.5.13 and earlier does not properly use the --status-fd argument when invoking GnuPG, which prevents Mutt from visually distinguishing between signed and unsigned portions of OpenPGP messages with multiple components, which allows remote attackers to forge the contents of a message without detection.
lists.gnupg.org/pipermail/gnupg-users/2007-March/030514.html
secunia.com/advisories/24415
securityreason.com/securityalert/2353
www.coresecurity.com/?action=item&id=1687
www.securityfocus.com/archive/1/461958/100/0/threaded
www.securityfocus.com/archive/1/461958/30/7710/threaded
www.securityfocus.com/bid/22778
www.securitytracker.com/id?1017727
www.vupen.com/english/advisories/2007/0835