CVE-2021-43538

Name: CVE-2021-43538
Creator: NVD / NIST
Published: 2021-12-08T22:15:09.677+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 4.3/10EPSS 1.16%

Last modified Jun 17, 2026

CVE-2021-43538 is a medium-severity vulnerability rated 4.3/10 on the CVSS scale. By misusing a race in our notification code, an attacker could have forcefully hidden the notification for pages that had received full screen and pointer lock access, which could have been used for spoofing attacks. This vulnerability affects Thunderbird < 91.4.0, Firefox ESR < 91.4.0, and Firefox < 95.. EPSS estimates a 1.16% chance of exploitation in the next 30 days.

Description

By misusing a race in our notification code, an attacker could have forcefully hidden the notification for pages that had received full screen and pointer lock access, which could have been used for spoofing attacks. This vulnerability affects Thunderbird < 91.4.0, Firefox ESR < 91.4.0, and Firefox < 95.

Metrics

CVSS 3.1

4.3/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N

EPSS Probability

1.16%

63.1th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-362

Affected Software

Vendor	Product	Versions
Mozilla	Firefox	< 95.0
Mozilla	Firefox Esr	< 91.4.0
Mozilla	Thunderbird	< 91.4.0
Debian	Debian Linux	9.0
Debian	Debian Linux	10.0
Debian	Debian Linux	11.0

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1739091Issue Tracking, Permissions Required, Vendor Advisory
https://lists.debian.org/debian-lts-announce/2021/12/msg00030.htmlMailing List, Third Party Advisory
https://lists.debian.org/debian-lts-announce/2022/01/msg00001.htmlMailing List, Third Party Advisory
https://security.gentoo.org/glsa/202202-03Third Party Advisory
https://security.gentoo.org/glsa/202208-14Third Party Advisory
https://www.debian.org/security/2021/dsa-5026Third Party Advisory
https://www.debian.org/security/2022/dsa-5034Third Party Advisory
https://www.mozilla.org/security/advisories/mfsa2021-52/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-53/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-54/Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1739091Issue Tracking, Permissions Required, Vendor Advisory
https://lists.debian.org/debian-lts-announce/2021/12/msg00030.htmlMailing List, Third Party Advisory
https://lists.debian.org/debian-lts-announce/2022/01/msg00001.htmlMailing List, Third Party Advisory
https://security.gentoo.org/glsa/202202-03Third Party Advisory
https://security.gentoo.org/glsa/202208-14Third Party Advisory
https://www.debian.org/security/2021/dsa-5026Third Party Advisory
https://www.debian.org/security/2022/dsa-5034Third Party Advisory
https://www.mozilla.org/security/advisories/mfsa2021-52/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-53/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-54/Vendor Advisory

Timeline

Published: Dec 8, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-43538?

How severe is CVE-2021-43538?

CVE-2021-43538 has a CVSS score of 4.3/10 (MEDIUM severity). The EPSS model estimates a 1.16% probability of exploitation in the next 30 days.

How do I fix CVE-2021-43538?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-43538?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST