A krb5 security update has been released for Debian GNU/Linux 9 LTS to address several vulnerabilities.

DLA 2771-1: krb5 security update

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Debian LTS Advisory DLA-2771-1 debian-lts@lists.debian.org
  https://www.debian.org/lts/security/ Adrian Bunk
September 30, 2021   https://wiki.debian.org/LTS
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Package : krb5
Version : 1.15-1+deb9u3
CVE ID : CVE-2018-5729 CVE-2018-5730 CVE-2018-20217 CVE-2021-37750
Debian Bug : 891869 917387 992607

Several vulnerabilities were fixed in MIT Kerberos,
a system for authenticating users and services on a network.

CVE-2018-5729
CVE-2018-5730

Fix flaws in LDAP DN checking.

CVE-2018-20217

Ignore password attributes for S4U2Self requests.

CVE-2021-37750

Fix KDC null deref on TGS inner body null server.

For Debian 9 stretch, these problems have been fixed in version
1.15-1+deb9u3.

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