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CVE-2017-7820 The "instanceof" operator can bypass the Xray wrapper mechanism

Description

The "instanceof" operator can bypass the Xray wrapper mechanism. When called on web content from the browser itself or an extension the web content can provide its own result for that operator, possibly tricking the browser or extension into mishandling the element. This vulnerability affects Firefox < 56.

Affected products and versions

Product Affected versions Fixed in
Firefox 56 earliest → < 56 56

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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