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CVE-2026-25896— fast-xml-parser has an entity encoding bypass via regex injection in DOCTYPE entity names

Quick assessment

Affected
NaturalIntelligence fast-xml-parser
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.

fast-xml-parser是Natural Intelligence开源的一个库。用于在没有基于 C/C++ 的库和回调的情况下，快速验证 XML、解析 XML 和构建 XML。 fast-xml-parser 4.1.3版本至5.3.5之前版本存在安全漏洞，该漏洞源于DOCTYPE实体名称中的点被当作正则表达式通配符处理，可能导致跨站脚本攻击。

CVSS 9.3 · Critical EPSS 0.50% · P41

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 2

VendorProduct Version RangeStatus
NaturalIntelligence fast-xml-parser >= 5.0.0, < 5.3.5 affected
>= 4.1.3, < 4.5.4 affected
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I. Basic Information for CVE-2026-25896

Vulnerability Information
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Vulnerability Title
fast-xml-parser has an entity encoding bypass via regex injection in DOCTYPE entity names
Source: CVE Program / CVE List V5
Vulnerability Description
fast-xml-parser allows users to validate XML, parse XML to JS object, or build XML from JS object without C/C++ based libraries and no callback. From 4.1.3to before 5.3.5, a dot (.) in a DOCTYPE entity name is treated as a regex wildcard during entity replacement, allowing an attacker to shadow built-in XML entities (&lt;, &gt;, &amp;, &quot;, &apos;) with arbitrary values. This bypasses entity encoding and leads to XSS when parsed output is rendered. This vulnerability is fixed in 5.3.5.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
不正确的正则表达式
Source: CVE Program / CVE List V5
Vulnerability Title
fast-xml-parser 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
fast-xml-parser是Natural Intelligence开源的一个库。用于在没有基于 C/C++ 的库和回调的情况下，快速验证 XML、解析 XML 和构建 XML。 fast-xml-parser 4.1.3版本至5.3.5之前版本存在安全漏洞，该漏洞源于DOCTYPE实体名称中的点被当作正则表达式通配符处理，可能导致跨站脚本攻击。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

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Affected Products

Vendor Product Affected Versions CPE Subscribe
NaturalIntelligence fast-xml-parser >= 5.0.0, < 5.3.5 -

II. Public POCs for CVE-2026-25896

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III. Intelligence Information for CVE-2026-25896

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Patches & Fixes for CVE-2026-25896 (1)

IV. Related Vulnerabilities

Same product: fast-xml-parser
Same vendor: NaturalIntelligence
Same weakness: CWE-185

V. Comments for CVE-2026-25896

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