A Firefox security update has been released for Ubuntu 18.04, 20.04 LTS, and 21.04.

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Ubuntu Security Notice USN-5074-1
September 09, 2021

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

- Ubuntu 21.04
- Ubuntu 20.04 LTS
- Ubuntu 18.04 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, bypass mixed
content blocking, or execute arbitrary code.

Update instructions:

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

Ubuntu 21.04:
firefox 92.0+build3-0ubuntu0.21.04.1

Ubuntu 20.04 LTS:
firefox 92.0+build3-0ubuntu0.20.04.1

Ubuntu 18.04 LTS:
firefox 92.0+build3-0ubuntu0.18.04.1

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

References:
  https://ubuntu.com/security/notices/USN-5074-1
CVE-2021-38491, CVE-2021-38493, CVE-2021-38494

Package Information:
  https://launchpad.net/ubuntu/+source/firefox/92.0+build3-0ubuntu0.21.04.1
  https://launchpad.net/ubuntu/+source/firefox/92.0+build3-0ubuntu0.20.04.1
  https://launchpad.net/ubuntu/+source/firefox/92.0+build3-0ubuntu0.18.04.1