A thunderbird security update has been released for both Debian GNU/Linux 10 and 11 to address multiple security issues.

DSA 4959-1: thunderbird security update

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Debian Security Advisory DSA-4959-1 security@debian.org
  https://www.debian.org/security/ Moritz Muehlenhoff
August 15, 2021   https://www.debian.org/security/faq
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Package : thunderbird
CVE ID : CVE-2021-29980 CVE-2021-29984 CVE-2021-29985
CVE-2021-29986 CVE-2021-29988 CVE-2021-29989

Multiple security issues were discovered in Thunderbird, which could
result in the execution of arbitrary code.

For the stable distribution (bullseye), these problems have been fixed in
version 1:78.13.0-1~deb11u1.

For the oldstable distribution (buster), these problems have been fixed in
version 1:78.13.0-1~deb10u1.

We recommend that you upgrade your thunderbird packages.

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

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/