An issue has been found in the parsing of authoritative answers in PowerDNS Recursor before 4.0.8, leading to a NULL pointer dereference when parsing a specially crafted answer containing a CNAME of a different class than IN. An unauthenticated remote attacker could cause a denial of service.
When api-config-dir is set to a non-empty value, which is not the case by default, the API in PowerDNS Recursor 4.x up to and including 4.0.6 and 3.x up to and including 3.7.4 allows an authorized user to update the Recursor's ACL by adding and removing netmasks, and to configure forward zones. It was discovered that the new netmask and IP addresses of forwarded zones were not sufficiently validated, allowing an authenticated user to inject new configuration directives into the Recursor's configuration.