HtmlUnit Neko up to 5.3.x HTML Serialization printCharacters HTML injection

Summaryinfo

A vulnerability categorized as problematic has been discovered in HtmlUnit Neko up to 5.3.x. This impacts the function printCharacters of the component HTML Serialization. The manipulation results in HTML injection. This vulnerability is reported as CVE-2026-104828. The attack can be launched remotely. No exploit exists. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in HtmlUnit Neko up to 5.3.x. It has been classified as problematic. Affected is the function printCharacters of the component HTML Serialization. The manipulation with an unknown input leads to a html injection vulnerability. CWE is classifying the issue as CWE-79. The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. This is going to have an impact on integrity. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability is traded as CVE-2026-104828 since 10/02/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. Successful exploitation requires user interaction by the victim. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1059.007.

Upgrading to version 5.4.0 eliminates this vulnerability.

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Productinfo

Vendor

• HtmlUnit

Name

• Neko

Version

• 5.0
• 5.1
• 5.2
• 5.3

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