A bind9 security update has been released for Debian GNU/Linux 10 ro address several vulnerabilities.

DSA 4909-1: bind9 security update

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Debian Security Advisory DSA-4909-1 security@debian.org
  https://www.debian.org/security/ Salvatore Bonaccorso
May 01, 2021   https://www.debian.org/security/faq
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Package : bind9
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 the stable distribution (buster), these problems have been fixed in
version 1:9.11.5.P4+dfsg-5.1+deb10u5.

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 Security Advisories, how to apply
these updates to your system and frequently asked questions can be
found at:   https://www.debian.org/security/