It was discovered that there was a buffer overflow attack in the
server caused by an issue in the GSSAPI (“Generic Security Services”) security
For Debian 8 Jessie, these problems have been fixed in version 1:9.9.5.dfsg-9+deb8u21.
We recommend that you upgrade your bind9 packages.
Further information about Extended LTS security advisories can be found at: https://deb.freexian.com/extended-lts/