What’s Vulnerable › Vulnerabilities

CVE-2021-38506

• Severity: medium (CVSS 4.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.5% 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-1021

Description

Through a series of navigations, Firefox could have entered fullscreen mode without notification or warning to the user. This could lead to spoofing attacks on the browser UI including phishing. This vulnerability affects Firefox < 94, Thunderbird < 91.3, and Firefox ESR < 91.3.

Affected products

• Debian Linux: 9.0, 10.0, 11.0
• Mozilla Firefox: before 94.0 — fixed in 94.0
• Mozilla Firefox ESR: before 91.3.0 — fixed in 91.3.0
• Mozilla Thunderbird: before 91.3.0 — fixed in 91.3.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 94.0; Mozilla Firefox ESR 91.3.0; Mozilla Thunderbird 91.3.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1730750
• 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/mfsa2021-48/
• https://www.mozilla.org/security/advisories/mfsa2021-49/
• https://www.mozilla.org/security/advisories/mfsa2021-50/
• https://bugzilla.mozilla.org/show_bug.cgi?id=1730750
• https://lists.debian.org/debian-lts-announce/2021/12/msg00030.html

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