Pyry Hakulinen and Ashish Shakla at Automattic discovered that pdns,
an authoritative DNS server, was incorrectly processing some DNS
packets; this would enable a remote attacker to trigger a DoS by
sending specially crafted packets causing the server to crash.
For the stable distribution (jessie), this problem has been fixed in
version 3.4.1-4+deb8u3.
For the testing distribution (stretch) and unstable distribution
(sid), this problem has been fixed in version 3.4.6-1.
We recommend that you upgrade your pdns packages.