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A GitHub-reviewed security advisory, not necessarily under active exploitation the way our CISA KEV advisories are, but a real, disclosed vulnerability in an open-source dependency.
Affected packages
Vulnerable: >= 8.1.0.beta1, < 8.1.4.1
Patched in 8.1.4.1
Vulnerable: < 8.0.5.2
Patched in 8.0.5.2
Details
ActionView::Helpers::TextHelper#highlight substitutes each matched phrase into the :highlighter string without escaping it and returns the result marked HTML-safe. Because sanitizing leaves quote characters in text unescaped, a match substituted into a quoted attribute value of the highlighter, such as the <a href="search?q=\1"> form shown in the method's documentation, could end the attribute value and add attributes to the element, possibly leading to XSS. Applications are affected when they pass a :highlighter that places a placeholder inside an attribute value and highlight text or phrases that a user controls. The default <mark>\1</mark> highlighter and the block form are not affected.
The fixed releases HTML-escape each group substituted into the :highlighter string, so quotes in a match are rendered as " and '. Only the numbered placeholders \0 to \9 are expanded; other String#sub replacement escapes, such as \k<name>, \& and \\, are left as written. A match can no longer begin on the > that closes a preceding tag. Escaping makes a placeholder safe as element content or inside a quoted attribute value, but not in an unquoted attribute value, a URL, JavaScript or CSS context, or an attribute whose value is HTML. See the Action View CHANGELOG for details.
Use a :highlighter that places the matched phrase only in element content, such as the default <mark>\1</mark>.
The fixed releases are available at the normal locations.
Patches for those who cannot upgrade at once:
This issue was found by the Anthropic OSS Scanner (ANT-2026-THHUJQVO).
EPSS, exploit probability
Low0.34%
estimated chance of real-world exploitation in the next 30 days, higher than 27.6% of every CVE FIRST.org scores
Refreshed 11/13/2026, via FIRST.org's EPSS model, not CVSS, this measures likelihood of exploitation, not how severe it would be.
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