The label decompression functionality in PowerDNS Recursor before 3.6.4 and 3.7.x before 3.7.3 and Authoritative (Auth) Server before 3.3.3 and 3.4.x before 3.4.5 allows remote attackers to cause a denial of service (CPU consumption or crash) via a request with a long name that refers to itself.  NOTE: this vulnerability exists because of an incomplete fix for CVE-2015-1868.