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CVE-2021-38509 Due to an unusual sequence of attacker-controlled events, a Javascript alert() dialog with arbitrary (although unstyled)…

Description

Due to an unusual sequence of attacker-controlled events, a Javascript alert() dialog with arbitrary (although unstyled) contents could be displayed over top an uncontrolled webpage of the attacker's choosing. 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-2026-118026 Invalid pointer in the JavaScript: GC component 8.8 High CVE-2026-118025 Other issue in the SVG component 8.8 High
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