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CVE-2026-26278— fast-xml-parser affected by DoS through entity expansion in DOCTYPE (no expansion limit)

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 5.3.5及之前版本存在安全漏洞，该漏洞源于XML解析器可能被迫进行无限量的实体扩展，可能导致正则表达式拒绝服务。

CVSS 7.5 · High EPSS 0.99% · P61

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking

Affected Version Matrix 2

VendorProduct Version RangeStatus
NaturalIntelligence fast-xml-parser >= 5.0.0, < 5.3.6 affected
>= 4.1.3, < 4.5.4 affected
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I. Basic Information for CVE-2026-26278

Vulnerability Information
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Vulnerability Title
fast-xml-parser affected by DoS through entity expansion in DOCTYPE (no expansion limit)
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. In versions 4.1.3 through 5.3.5, the XML parser can be forced to do an unlimited amount of entity expansion. With a very small XML input, it’s possible to make the parser spend seconds or even minutes processing a single request, effectively freezing the application. Version 5.3.6 fixes the issue. As a workaround, avoid using DOCTYPE parsing by `processEntities: false` option.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
DTD中递归实体索引的不恰当限制(XML实体扩展)
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 5.3.5及之前版本存在安全漏洞，该漏洞源于XML解析器可能被迫进行无限量的实体扩展，可能导致正则表达式拒绝服务。
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)

Affected Products

Vendor Product Affected Versions CPE Subscribe
NaturalIntelligence fast-xml-parser >= 5.0.0, < 5.3.6 -

II. Public POCs for CVE-2026-26278

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III. Intelligence Information for CVE-2026-26278

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Patches & Fixes for CVE-2026-26278 (1)

Vendor Advisories for CVE-2026-26278 (1)

IV. Related Vulnerabilities

Same product: fast-xml-parser
Same vendor: NaturalIntelligence
Same weakness: CWE-776

V. Comments for CVE-2026-26278

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