A libreswan security update has been released for Debian GNU/Linux 11 to address a denial of service issue.

DSA 5048-1: libreswan security update

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Debian Security Advisory DSA-5048-1 security@debian.org
  https://www.debian.org/security/ Salvatore Bonaccorso
January 15, 2022   https://www.debian.org/security/faq
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Package : libreswan
CVE ID : CVE-2022-23094

It was discovered that the libreswan IPsec implementation could be
forced into a crash/restart via a malformed IKEv1 packet, resulting in
denial of service.

For the stable distribution (bullseye), this problem has been fixed in
version 4.3-1+deb11u1.

We recommend that you upgrade your libreswan packages.

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

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/