Kerio Personal Firewall (KPF) 2.1.4 has a default rule to accept incoming packets from DNS (UDP port 53), which allows remote attackers to bypass the firewall filters via packets with a source port of 53.
https://exchange.xforce.ibmcloud.com/vulnerabilities/11880
http://www.securityfocus.com/bid/7436
http://www.securiteam.com/securitynews/5FP0N1P9PI.html
http://archives.neohapsis.com/archives/fulldisclosure/2003-q2/0352.html