CVE-2021-38496: Use After Free

Published Oct 5, 2021
·
Updated

During operations on MessageTasks, a task may have been removed while it was still scheduled, resulting in memory corruption and a potentially exploitable crash.

Affected Software

48 affected componentsFixes available
debian/firefox
118.0.2-1
debian/firefox-esr
91.12.0esr-1~deb10u1115.3.1esr-1~deb10u1102.15.0esr-1~deb11u1115.3.1esr-1~deb11u1102.15.1esr-1~deb12u1115.3.0esr-1~deb12u1115.3.0esr-1115.4.0esr-1
debian/thunderbird
1:91.12.0-1~deb10u11:115.3.1-1~deb10u11:102.13.1-1~deb11u11:115.3.1-1~deb11u11:102.15.1-1~deb12u11:115.3.1-1~deb12u11:115.3.1-1
Mozilla Thunderbird<91.2
91.2
Mozilla Firefox<93
93
Mozilla Firefox ESR<91.2
91.2
Mozilla Firefox ESR<78.15
78.15
Mozilla Firefox<93.0
Mozilla Firefox>=91.0<91.2
Mozilla Firefox ESR<78.15
Mozilla Thunderbird<78.15
Mozilla Thunderbird>=91.0<91.2
Debian Debian Linux=9.0
Debian Debian Linux=10.0
Debian Debian Linux=11.0
Mozilla Firefox ESR>=91.0<91.2
alpine/firefox>=91.0<93.0-r0
93.0-r0
alpine/firefox>=91.0<93.0-r0
93.0-r0
alpine/firefox>=91.0<93.0-r0
93.0-r0
alpine/firefox>=91.0<93.0-r0
93.0-r0
alpine/firefox>=91.0<93.0-r0
93.0-r0
alpine/firefox>=91.0<93.0-r0
93.0-r0
alpine/firefox>=91.0<93.0-r0
93.0-r0
alpine/firefox>=91.0<93.0-r0
93.0-r0
alpine/firefox>=91.0<93.0-r0
93.0-r0
alpine/firefox-esr<78.15.0-r0
78.15.0-r0
alpine/firefox-esr<78.15.0-r0
78.15.0-r0
alpine/firefox-esr<91.2.0-r0
91.2.0-r0
alpine/firefox-esr<91.2.0-r0
91.2.0-r0
alpine/firefox-esr<91.2.0-r0
91.2.0-r0
alpine/firefox-esr<91.2.0-r0
91.2.0-r0
alpine/firefox-esr<91.2.0-r0
91.2.0-r0
alpine/firefox-esr<91.2.0-r0
91.2.0-r0
alpine/firefox-esr<91.2.0-r0
91.2.0-r0
alpine/firefox-esr<91.2.0-r0
91.2.0-r0
alpine/firefox-esr<91.2.0-r0
91.2.0-r0
alpine/librewolf<93.0-r0
93.0-r0
alpine/librewolf<93.0-r0
93.0-r0
alpine/librewolf<93.0-r0
93.0-r0
alpine/librewolf<93.0-r0
93.0-r0
alpine/thunderbird>=91.0<91.3.2-r0
91.3.2-r0
alpine/thunderbird>=91.0<91.3.2-r0
91.3.2-r0
alpine/thunderbird>=91.0<91.3.2-r0
91.3.2-r0
alpine/thunderbird>=91.0<91.3.2-r0
91.3.2-r0
alpine/thunderbird>=91.0<91.3.2-r0
91.3.2-r0
alpine/thunderbird>=91.0<91.3.2-r0
91.3.2-r0
alpine/thunderbird>=91.0<91.3.2-r0
91.3.2-r0
alpine/thunderbird>=91.0<91.3.2-r0
91.3.2-r0

Remediation

Recommended actions to resolve this vulnerability, in priority order.

  1. Upgrade

    Upgrade debian/firefox to a version that resolves this vulnerability.

    Fixed in 118.0.2-1
  2. Upgrade

    Upgrade debian/firefox-esr to a version that resolves this vulnerability.

    Fixed in 91.12.0esr-1~deb10u1Fixed in 115.3.1esr-1~deb10u1Fixed in 102.15.0esr-1~deb11u1Fixed in 115.3.1esr-1~deb11u1Fixed in 102.15.1esr-1~deb12u1Fixed in 115.3.0esr-1~deb12u1Fixed in 115.3.0esr-1Fixed in 115.4.0esr-1
  3. Upgrade

    Upgrade debian/thunderbird to a version that resolves this vulnerability.

    Fixed in 1:91.12.0-1~deb10u1Fixed in 1:115.3.1-1~deb10u1Fixed in 1:102.13.1-1~deb11u1Fixed in 1:115.3.1-1~deb11u1Fixed in 1:102.15.1-1~deb12u1Fixed in 1:115.3.1-1~deb12u1Fixed in 1:115.3.1-1
  4. Upgrade

    Upgrade Thunderbird to a version that resolves this vulnerability.

    Fixed in 91.2
  5. Upgrade

    Upgrade Firefox to a version that resolves this vulnerability.

    Fixed in 93
  6. Upgrade

    Upgrade Firefox ESR to a version that resolves this vulnerability.

    Fixed in 91.2
  7. Upgrade

    Upgrade Firefox ESR to a version that resolves this vulnerability.

    Fixed in 78.15
  8. Upgrade

    Upgrade alpine/firefox to a version that resolves this vulnerability.

    Fixed in 93.0-r0
  9. Upgrade

    Upgrade alpine/firefox-esr to a version that resolves this vulnerability.

    Fixed in 78.15.0-r0
  10. Upgrade

    Upgrade alpine/firefox-esr to a version that resolves this vulnerability.

    Fixed in 91.2.0-r0
  11. Upgrade

    Upgrade alpine/librewolf to a version that resolves this vulnerability.

    Fixed in 93.0-r0
  12. Upgrade

    Upgrade alpine/thunderbird to a version that resolves this vulnerability.

    Fixed in 91.3.2-r0
  13. Upgrade

    Upgrade Thunderbird to a version that resolves this vulnerability.

    Fixed in 78.15

Event History

Oct 5, 2021
CVE Published
via Mozilla·12:00 AM
Nov 3, 2021
CVE Published
via MITRE·12:03 AM
Data Sourced
via MITRE·12:03 AM
DescriptionWeakness
Data Sourced
via NVD·01:15 AM
DescriptionSeverityWeaknessAffected Software
Data Sourced
via OSV·01:15 AM
DescriptionSeverityAffected Software

Parent advisories

This vulnerability appears in the following advisories.

Peer vulnerabilities

Found alongside the following vulnerabilities.

Frequently Asked Questions

1

What is CVE-2021-38496?

CVE-2021-38496 is a vulnerability that may result in memory corruption and a potentially exploitable crash in Thunderbird and Firefox.

2

Which software versions are affected by CVE-2021-38496?

CVE-2021-38496 affects Thunderbird < 78.15, Thunderbird < 91.2, Firefox ESR < 91.2, Firefox ESR < 78.15, and Firefox < 93.

3

What is the severity of CVE-2021-38496?

CVE-2021-38496 has a severity rating of 8.8 (high).

4

How can I fix CVE-2021-38496?

To fix CVE-2021-38496, it is recommended to update Thunderbird and Firefox to the latest available versions.

5

Where can I find more information about CVE-2021-38496?

You can find more information about CVE-2021-38496 on the Mozilla Bugzilla and Mozilla Security Advisories websites, as well as the Debian LTS Announce mailing list.

Company

Resources

Contact

SecAlerts Pty Ltd.
132 Wickham Terrace
Fortitude Valley,
QLD 4006, Australia
info@secalerts.co
By using SecAlerts services, you agree to our services end-user license agreement. This website is safeguarded by reCAPTCHA and governed by the Google Privacy Policy and Terms of Service. All names, logos, and brands of products are owned by their respective owners, and any usage of these names, logos, and brands for identification purposes only does not imply endorsement. If you possess any content that requires removal, please get in touch with us.
© 2026 SecAlerts Pty Ltd.
ABN: 70 645 966 203, ACN: 645 966 203