A krb5 security update has been released for Debian GNU/Linux 10 to address a denial of service issue.

DSA 4944-1: krb5 security update

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Debian Security Advisory DSA-4944-1 security@debian.org
  https://www.debian.org/security/ Salvatore Bonaccorso
July 25, 2021   https://www.debian.org/security/faq
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Package : krb5
CVE ID : CVE-2021-36222
Debian Bug : 991365

It was discovered that the Key Distribution Center (KDC) in krb5, the
MIT implementation of Kerberos, is prone to a NULL pointer dereference
flaw. An unauthenticated attacker can take advantage of this flaw to
cause a denial of service (KDC crash) by sending a request containing a
PA-ENCRYPTED-CHALLENGE padata element without using FAST.

For the stable distribution (buster), this problem has been fixed in
version 1.17-3+deb10u2.

We recommend that you upgrade your krb5 packages.

For the detailed security status of krb5 please refer to its security
tracker page at:
  https://security-tracker.debian.org/tracker/krb5

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/