A postorius security update has been released for Debian GNU/Linux 10 and 11 to address an issue where Postorius didn't validate whether a logged-in user owns the email address when unsubscribing.

DSA 4970-1: postorius security update

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Debian Security Advisory DSA-4970-1 security@debian.org
  https://www.debian.org/security/ Moritz Muehlenhoff
September 09, 2021   https://www.debian.org/security/faq
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Package : postorius
CVE ID : CVE-2021-40347

Kevin Israel discovered that Postorius, the administrative web frontend
for Mailman 3, didn't validate whether a logged-in user owns the email
address when unsubscribing.

For the oldstable distribution (buster), this problem has been fixed
in version 1.2.4-1+deb10u1.

For the stable distribution (bullseye), this problem has been fixed in
version 1.3.4-2+deb11u1.

We recommend that you upgrade your postorius packages.

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

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/