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CVE-2026-104828

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

7.2 High

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.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
Low
Integrity
Low
Availability
None

Exploit likelihood

0.32%Up 0.1 points since Oct 16, 2026
90%50%10%1%

What each source reports

CVE List Score used 7.2

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

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.

Record
CVE-2026-104828
CVSS 3.1
7.2 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
Weakness
CWE-79
Updated
2026-11-02
EUVDEUVD-2026-102316 7.2

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.

Record
EUVD-2026-102316
CVSS 3.1
7.2 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
Updated
2026-11-02
NVD 7.2

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.

Record
CVE-2026-104828
CVSS 3.1
7.2 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
Weakness
CWE-79
Updated
2026-11-02
OSV 7.2

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

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.

Record
CVE-2026-104828
CVSS 3.1
7.2 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
Weakness
CWE-79
Updated
2026-11-02

Affected products

History

History
RecordedChangedSources
first indexedCVE List, EUVD, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-104828 is a high vulnerability (CVSS 7.2) in Htmlunit Htmlunit-neko, published October 15, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.32%, the 25th percentile. No source names a fixed version.

References

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