A firefox-esr security update has been released for Debian GNU/Linux 9 LTS to address multiple security issues.

DLA 2607-1: firefox-esr security update

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Debian LTS Advisory DLA-2607-1 debian-lts@lists.debian.org
  https://www.debian.org/lts/security/ Emilio Pozuelo Monfort
March 25, 2021   https://wiki.debian.org/LTS
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Package : firefox-esr
Version : 78.9.0esr-1~deb9u1
CVE ID : CVE-2021-23981 CVE-2021-23982 CVE-2021-23984 CVE-2021-23987

Multiple security issues have been found in the Mozilla Firefox
web browser, which could potentially result in the execution
of arbitrary code, information disclosure or spoofing attacks.

For Debian 9 stretch, these problems have been fixed in version
78.9.0esr-1~deb9u1.

We recommend that you upgrade your firefox-esr packages.

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

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