A Firefox regressions update has been released for Ubuntu Linux 18.04 LTS, 20.04 LTS, 21.04, and 21.10.

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Ubuntu Security Notice USN-5186-2
December 20, 2021

firefox regressions
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A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 21.10
- Ubuntu 21.04
- Ubuntu 20.04 LTS
- Ubuntu 18.04 LTS

Summary:

USN-5186-1 caused some minor regressions in Firefox.

Software Description:
- firefox: Mozilla Open Source web browser

Details:

USN-5186-1 fixed vulnerabilities in Firefox. The update introduced several
minor regressions. This update fixes the problem.

We apologize for the inconvenience.

Original advisory details:

Multiple security issues were discovered in Firefox. If a user were
tricked into opening a specially crafted website, an attacker could
potentially exploit these to cause a denial of service, obtain sensitive
information, conduct spoofing attacks, bypass CSP restrictions, or
execute arbitrary code. (CVE-2021-43536, CVE-2021-43537, CVE-2021-43538,
CVE-2021-43539, CVE-2021-43541, CVE-2021-43542, CVE-2021-43543,
CVE-2021-43545, CVE-2021-43546)
A security issue was discovered with the handling of WebExtension
permissions. If a user were tricked into installing a specially crafted
extension, an attacker could potentially exploit this to create and
install a service worker that wouldn't be uninstalled with the extension.
(CVE-2021-43540)

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 21.10:
firefox 95.0.1+build2-0ubuntu0.21.10.1

Ubuntu 21.04:
firefox 95.0.1+build2-0ubuntu0.21.04.1

Ubuntu 20.04 LTS:
firefox 95.0.1+build2-0ubuntu0.20.04.1

Ubuntu 18.04 LTS:
firefox 95.0.1+build2-0ubuntu0.18.04.1

After a standard system update you need to restart Firefox to make
all the necessary changes.

References:
  https://ubuntu.com/security/notices/USN-5186-2
  https://ubuntu.com/security/notices/USN-5186-1
  https://launchpad.net/bugs/1955433

Package Information:

  https://launchpad.net/ubuntu/+source/firefox/95.0.1+build2-0ubuntu0.21.10.1

  https://launchpad.net/ubuntu/+source/firefox/95.0.1+build2-0ubuntu0.21.04.1

  https://launchpad.net/ubuntu/+source/firefox/95.0.1+build2-0ubuntu0.20.04.1

  https://launchpad.net/ubuntu/+source/firefox/95.0.1+build2-0ubuntu0.18.04.1