What’s Vulnerable › Vulnerabilities

CVE-2026-104828: HtmlUnit Neko: Mutation XSS (mXSS) in HTMLWriterFilter - TEXTAREA/TITLE entity decode without re-encode

• Severity: high (CVSS 7.2 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-15 · updated 2026-10-21
• Weakness: CWE-79

Description

HtmlUnit Neko is an HtmlUnit adaptation of NekoHTML. Prior to 5.4.0, HTMLWriterFilter writes decoded TEXTAREA and TITLE character content without entity encoding because both elements are treated as special content. During a parse-and-serialize round trip, entity references inside these escapable raw-text elements are decoded by the parser and then emitted as raw markup by printCharacters(), changing the document's semantics. Applications that use htmlunit-neko in an HTML sanitizer, content filter, or other parse-transform-serialize pipeline can therefore turn attacker-controlled encoded text into executable markup when the output is rendered by a browser. This issue is fixed in version 5.4.0.

Affected products

• htmlunit-neko: before 5.4.0

References

• https://github.com/HtmlUnit/htmlunit-neko/commit/c165891e0753aef3e05f5daa6250d3e8d4ada3c0
• https://github.com/HtmlUnit/htmlunit-neko/releases/tag/5.4.0
• https://github.com/HtmlUnit/htmlunit-neko/security/advisories/GHSA-39xg-prhf-8785
• https://github.com/HtmlUnit/htmlunit-neko/security/advisories/GHSA-39xg-prhf-8785

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