What’s Vulnerable › Vulnerabilities

CVE-2021-43538

• Severity: medium (CVSS 4.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-12-08 · updated 2026-06-17
• Weakness: CWE-362

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.

Affected products

• Debian Linux: 9.0, 10.0, 11.0
• Mozilla Firefox: before 95.0 — fixed in 95.0
• Mozilla Firefox ESR: before 91.4.0 — fixed in 91.4.0
• Mozilla Thunderbird: before 91.4.0 — fixed in 91.4.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 95.0; Mozilla Firefox ESR 91.4.0; Mozilla Thunderbird 91.4.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1739091
• https://lists.debian.org/debian-lts-announce/2021/12/msg00030.html
• https://lists.debian.org/debian-lts-announce/2022/01/msg00001.html
• https://security.gentoo.org/glsa/202202-03
• https://security.gentoo.org/glsa/202208-14
• https://www.debian.org/security/2021/dsa-5026
• https://www.debian.org/security/2022/dsa-5034
• https://www.mozilla.org/security/advisories/mfsa2021-52/
• https://www.mozilla.org/security/advisories/mfsa2021-53/
• https://www.mozilla.org/security/advisories/mfsa2021-54/
• https://bugzilla.mozilla.org/show_bug.cgi?id=1739091
• https://lists.debian.org/debian-lts-announce/2021/12/msg00030.html

Get alerted when CVE-2021-43538 or the next vulnerability affects your stack