A bind9 security update has been released for Debian 6 LTS

Package : bind9
Version : 1:9.7.3.dfsg-1~squeeze17
CVE ID : CVE-2015-5722

Hanno Böck from the Fuzzing Project discovered that incorrect validation of
DNSSEC-signed records in the Bind DNS server could result in denial of service.

For Debian 6 “Squeeze”, this issue has been fixed in bind9 version
1:9.7.3.dfsg-1~squeeze17. We recomend you to upgrade your bind9 packages.

Learn more about the Debian Long Term Support (LTS) Project and how to
apply these updates at: https://wiki.debian.org/LTS/