X11 in Apple Mac OS X 10.5 through 10.5.1 does not properly handle when the "Allow connections from network client" preference is disabled, which allows remote attackers to bypass intended access restrictions and connect to the X server.
http://www.vupen.com/english/advisories/2008/0495/references
http://www.us-cert.gov/cas/techalerts/TA08-043B.html
http://www.securitytracker.com/id?1019365
http://www.securityfocus.com/bid/27736
http://secunia.com/advisories/28891
http://lists.apple.com/archives/security-announce/2008/Feb/msg00002.html