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

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Ubuntu Security Notice USN-4926-1
April 26, 2021

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

- Ubuntu 20.04
- 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, spoof the
browser UI, bypass security restrictions, trick the user into disclosing
confidential information, or execute arbitrary code. (CVE-2021-23994,
CVE-2021-23996, CVE-2021-23997, CVE-2021-23998, CVE-2021-23999,
CVE-2021-24000, CVE-2021-24001, CVE-2021-29945, CVE-2021-29946,
CVE-2021-29947)

A use-after-free was discovered when Responsive Design Mode was
enabled. If a user were tricked into opening a specially crafted
website with Responsive Design Mode enabled, an attacker could
potentially exploit this to cause a denial of service, or execute
arbitrary code. (CVE-2021-23995)

It was discovered that Firefox mishandled ftp URLs with encoded newline
characters. If a user were tricked into clicking on a specially crafted
link, an attacker could potentially exploit this to send arbitrary
FTP commands. (CVE-2021-24002)

Update instructions:

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

Ubuntu 20.04:
firefox 88.0+build2-0ubuntu0.21.04.1

Ubuntu 20.10:
firefox 88.0+build2-0ubuntu0.20.10.1

Ubuntu 20.04 LTS:
firefox 88.0+build2-0ubuntu0.20.04.1

Ubuntu 18.04 LTS:
firefox 88.0+build2-0ubuntu0.18.04.2

Ubuntu 16.04 LTS:
firefox 88.0+build2-0ubuntu0.16.04.1

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

References:
  https://ubuntu.com/security/notices/USN-4926-1
CVE-2021-23994, CVE-2021-23995, CVE-2021-23996, CVE-2021-23997,
CVE-2021-23998, CVE-2021-23999, CVE-2021-24000, CVE-2021-24001,
CVE-2021-24002, CVE-2021-29945, CVE-2021-29946, CVE-2021-29947

Package Information:
  https://launchpad.net/ubuntu/+source/firefox/88.0+build2-0ubuntu0.21.04.1
  https://launchpad.net/ubuntu/+source/firefox/88.0+build2-0ubuntu0.20.10.1
  https://launchpad.net/ubuntu/+source/firefox/88.0+build2-0ubuntu0.20.04.1
  https://launchpad.net/ubuntu/+source/firefox/88.0+build2-0ubuntu0.18.04.2
  https://launchpad.net/ubuntu/+source/firefox/88.0+build2-0ubuntu0.16.04.1