A c-ares security update has been released for Debian GNU/Linux 10 to address a missing input validation of host names.

DSA 4954-1: c-ares security update

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Debian Security Advisory DSA-4954-1 security@debian.org
  https://www.debian.org/security/ Salvatore Bonaccorso
August 10, 2021   https://www.debian.org/security/faq
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Package : c-ares
CVE ID : CVE-2021-3672
Debian Bug : 992053

Philipp Jeitner and Haya Shulman discovered a flaw in c-ares, a library
that performs DNS requests and name resolution asynchronously. Missing
input validation of hostnames returned by DNS servers can lead to output
of wrong hostnames (leading to Domain Hijacking).

For the stable distribution (buster), this problem has been fixed in
version 1.14.0-1+deb10u1.

We recommend that you upgrade your c-ares packages.

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

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/