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9.1 Critical

CVE-2025-6427 An attacker was able to bypass the `connect-src` directive of a Content Security Policy by manipulating subdocuments

Description

An attacker was able to bypass the `connect-src` directive of a Content Security Policy by manipulating subdocuments. This would have also hidden the connections from the Network tab in Devtools. This vulnerability was fixed in Firefox 140 and Thunderbird 140.

Affected products and versions

Product Affected versions Fixed in
Firefox 140 earliest → < 140 140
Thunderbird 140 earliest → < 140 140

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-2026-118025 Other issue in the SVG component 8.8 High CVE-2026-118026 Invalid pointer in the JavaScript: GC component 8.8 High
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