A bind9 regression update has been released to address a regression in the previous update.

DLA 2955-2: bind9 regression update

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Debian LTS Advisory DLA-2955-2 debian-lts@lists.debian.org
  https://www.debian.org/lts/security/ Markus Koschany
March 19, 2022   https://wiki.debian.org/LTS
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Package : bind9
Version : 1:9.10.3.dfsg.P4-12.3+deb9u12
CVE ID : CVE-2021-25220
Debian Bug : 1007945

The security update announced as DLA 2955-1 caused a regression in named due to
an incomplete fix for CVE-2021-25220 when the Forwarders option was configured.
Updated bind9 packages are now available to correct this issue.

For Debian 9 stretch, this problem has been fixed in version
1:9.10.3.dfsg.P4-12.3+deb9u12.

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