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CVE-2021-38506 Through a series of navigations, Firefox could have entered fullscreen mode without notification or warning to the user

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 and versions

Product Affected versions Fixed in
Firefox 94 earliest → < 94 94
Thunderbird 91.3 earliest → < 91.3 91.3
Firefox ESR 91.3 earliest → < 91.3 91.3

Other CVEs of Firefox

The 2221 CVEs of Firefox →
CVE-2026-120572 Incorrect boundary conditions in the Layout: Block and Inline component 8.8 High CVE-2026-118027 Frame poisoning in the Layout component 9.1 Critical CVE-2026-118024 Use-after-free in the Graphics: Text component 8.8 High CVE-2026-118025 Other issue in the SVG component 8.8 High
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