xhtml-purifier has HTML attribute-injection (sanitizer bypass) that leads to XSS
Summary
CVE-2026-61784: xhtml-purifier has HTML attribute-injection (sanitizer bypass) that leads to XSS. Affects xhtml-purifier versions < 0.4.3. Fixed in 0.4.3. How to fix ↓
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xhtml-purifier does not HTML-entity-encode attribute values when serializing its sanitized output. In attributeString() (XHTMLPurifier.js, around line 148) the attribute value is concatenated directly into a double-quoted attribute without encoding. As a result, an attacker-controlled value in any allowed attribute (class, style, title, alt, src, href) can include a double-quote character to break out of the attribute and inject an additional attribute, such as a JavaScript event handler (for example onmouseover or onerror). The injected handler survives sanitization and executes when the output is rendered, which is a sanitizer bypass leading to cross-site scripting. The fix HTML-entity-encodes attribute values before serialization.
How To Fix
Minimum fixed version
0.4.3
This is the first release that contains the fix.
npm install xhtml-purifier@0.4.3Tip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
