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CVE-2020-26958 Firefox did not block execution of scripts with incorrect MIME types when the response was intercepted and cached…

Description

Firefox did not block execution of scripts with incorrect MIME types when the response was intercepted and cached through a ServiceWorker. This could lead to a cross-site script inclusion vulnerability, or a Content Security Policy bypass. This vulnerability affects Firefox < 83, Firefox ESR < 78.5, and Thunderbird < 78.5.

Affected products and versions

Product Affected versions Fixed in
Firefox 83 earliest → < 83 83
Firefox ESR 78.5 earliest → < 78.5 78.5
Thunderbird 78.5 earliest → < 78.5 78.5

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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