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

Quick assessment

Affected
HtmlUnit htmlunit-neko
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

HtmlUnit Neko 是基于 NekoHTML 对 HtmlUnit 的一种适配实现。在 5.4.0 版本之前， 在对 和 元素的解码后文本内容进行写入时，未进行实体编码（entity encoding），因为这两个元素被视为特殊内容类型。在“解析—序列化”往返过程中，这些可转义原始文本（raw-text）元素内部的实体引用会被解析器解码，随后由 方法作为原始标记直接输出，从而改变文档的语义。因此，若应用程序将 htmlunit-neko 用于 HTML 清理器（HTML sanitizer）、内容过滤器或其

CVSS 7.2 · High EPSS 0.26% · P17

Affected Version Matrix 1

VendorProduct Version RangeStatus
HtmlUnit htmlunit-neko < 5.4.0 affected
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I. Basic Information for CVE-2026-104828

Vulnerability Information
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Vulnerability Title
HtmlUnit Neko: Mutation XSS (mXSS) in HTMLWriterFilter - TEXTAREA/TITLE entity decode without re-encode
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
在Web页面生成时对输入的转义处理不恰当(跨站脚本)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
HtmlUnit htmlunit-neko < 5.4.0 -

II. Public POCs for CVE-2026-104828

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III. Intelligence Information for CVE-2026-104828

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Patches & Fixes for CVE-2026-104828 (1)

Vendor Advisories for CVE-2026-104828 (1)

Vendor Pages for CVE-2026-104828 (1)

IV. Related Vulnerabilities

Same vendor: HtmlUnit
Same weakness: CWE-79

V. Comments for CVE-2026-104828

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