A Firefox security update has been released for Ubuntu Linux 16.04 LTS, 18.04 LTS, 20.04 LTS, and 20.10.

==========================================================================
Ubuntu Security Notice USN-4671-1
December 15, 2020

firefox vulnerabilities
==========================================================================

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

- Ubuntu 20.10
- Ubuntu 20.04 LTS
- Ubuntu 18.04 LTS
- Ubuntu 16.04 LTS

Summary:

Firefox could be made to crash or run programs as your login if it
opened a malicious website.

Software Description:
- firefox: Mozilla Open Source web browser

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, bypass the CSS sanitizer, bypass security restrictions,
spoof the URL bar, or execute arbitrary code. (CVE-2020-16042,
CVE-2020-26971, CVE-2020-26972, CVE-2020-26793, CVE-2020-26974,
CVE-2020-26976, CVE-2020-26978, CVE-2020-26979,
CVE-2020-35113, CVE-2020-35114)

It was discovered that the proxy.onRequest API did not catch
view-source URLs. If a user were tricked in to installing an
extension with the proxy permission and opening View Source, an
attacker could potentially exploit this to obtain sensitive
information. (CVE-2020-35111)

Update instructions:

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

Ubuntu 20.10:
firefox 84.0+build3-0ubuntu0.20.10.1

Ubuntu 20.04 LTS:
firefox 84.0+build3-0ubuntu0.20.04.1

Ubuntu 18.04 LTS:
firefox 84.0+build3-0ubuntu0.18.04.1

Ubuntu 16.04 LTS:
firefox 84.0+build3-0ubuntu0.16.04.1

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

References:
  https://usn.ubuntu.com/4671-1
CVE-2020-16042, CVE-2020-26971, CVE-2020-26972, CVE-2020-26973,
CVE-2020-26974, CVE-2020-26976, CVE-2020-26978, CVE-2020-26979,
CVE-2020-35111, CVE-2020-35113, CVE-2020-35114

Package Information:
  https://launchpad.net/ubuntu/+source/firefox/84.0+build3-0ubuntu0.20.10.1
  https://launchpad.net/ubuntu/+source/firefox/84.0+build3-0ubuntu0.20.04.1
  https://launchpad.net/ubuntu/+source/firefox/84.0+build3-0ubuntu0.18.04.1
  https://launchpad.net/ubuntu/+source/firefox/84.0+build3-0ubuntu0.16.04.1