A bind9 security update has been released for Debian GNU/Linux 9 LTS to address several vulnerabilities.

DLA 2647-1: bind9 security update

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Debian LTS Advisory DLA-2647-1 debian-lts@lists.debian.org
  https://www.debian.org/lts/security/ Emilio Pozuelo Monfort
May 04, 2021   https://wiki.debian.org/LTS
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Package : bind9
Version : 1:9.10.3.dfsg.P4-12.3+deb9u9
CVE ID : CVE-2021-25214 CVE-2021-25215 CVE-2021-25216
Debian Bug : 987741 987742 987743

Several vulnerabilities were discovered in BIND, a DNS server
implementation.

CVE-2021-25214

Greg Kuechle discovered that a malformed incoming IXFR transfer
could trigger an assertion failure in named, resulting in denial
of service.

CVE-2021-25215

Siva Kakarla discovered that named could crash when a DNAME record
placed in the ANSWER section during DNAME chasing turned out to be
the final answer to a client query.

CVE-2021-25216

It was discovered that the SPNEGO implementation used by BIND is
prone to a buffer overflow vulnerability. This update switches to
use the SPNEGO implementation from the Kerberos libraries.

For Debian 9 stretch, these problems have been fixed in version
1:9.10.3.dfsg.P4-12.3+deb9u9.

We recommend that you upgrade your bind9 packages.

For the detailed security status of bind9 please refer to
its security tracker page at:
  https://security-tracker.debian.org/tracker/bind9

Further information about Debian LTS security advisories, how to apply
these updates to your system and frequently asked questions can be
found at:   https://wiki.debian.org/LTS