Simple DNS Plus 4.1, 5.0, and possibly other versions before 5.1.101 allows remote attackers to cause a denial of service via multiple DNS reply packets.
https://www.exploit-db.com/exploits/6059
https://exchange.xforce.ibmcloud.com/vulnerabilities/43767
http://www.simpledns.com/kb.aspx?kbid=1246
http://www.securityfocus.com/bid/30207
http://www.securityfocus.com/archive/1/494304/100/0/threaded