Shorewall 2.4.x before 2.4.1, 2.2.x before 2.2.5, and 2.0.x before 2.0.17, when MACLIST_TTL is greater than 0 or MACLIST_DISPOSITION is set to ACCEPT, allows remote attackers with an accepted MAC address to bypass other firewall rules or policies.
http://www.ubuntu.com/usn/usn-197-1
http://www.securityfocus.com/bid/14292
http://www.gentoo.org/security/en/glsa/glsa-200507-20.xml
http://www.debian.org/security/2005/dsa-849
http://shorewall.net/News.htm#20050717
http://secunia.com/advisories/17113
http://secunia.com/advisories/17110