PowerDNS Recursor 3.1.3 and earlier allows remote attackers to cause a denial of service (resource exhaustion and application crash) via a CNAME record with a zero TTL, which triggers an infinite loop.
https://exchange.xforce.ibmcloud.com/vulnerabilities/30257
http://www.vupen.com/english/advisories/2006/4484
http://www.securityfocus.com/bid/21037
http://secunia.com/advisories/22976
http://secunia.com/advisories/22824
http://lists.suse.com/archive/suse-security-announce/2006-Nov/0007.html