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CVE-2026-34401— XML Notepad: XML External Entity (XXE) Injection via Unsafe XmlTextReader in XML Diff and Schema Loading

Quick assessment

Affected
microsoft XmlNotepad
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.

XmlNotepad是Microsoft开源的一个XML文档浏览与编辑工具。 XmlNotepad 2.9.0.21之前版本存在代码问题漏洞，该漏洞源于默认未禁用DTD处理，可能导致解析恶意XML文件时泄露本地文件内容或凭据。

CVSS 6.5 · Medium EPSS 1.39% · P72
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I. Basic Information for CVE-2026-34401

Vulnerability Information
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Vulnerability Title
XML Notepad: XML External Entity (XXE) Injection via Unsafe XmlTextReader in XML Diff and Schema Loading
Source: CVE Program / CVE List V5
Vulnerability Description
XML Notepad is a Windows program that provides a simple intuitive User Interface for browsing and editing XML documents. Prior to version 2.9.0.21, XML Notepad does not disable DTD processing by default which means external entities are resolved automatically. There is a well known attack related to malicious DTD files where an attacker to craft a malicious XML file that loads a DTD that causes XML Notepad to make outbound HTTP/SMB requests, potentially leaking local file contents or capturing the victim's NTLM credentials. This issue has been patched in version 2.9.0.21.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
XML外部实体引用的不恰当限制(XXE)
Source: CVE Program / CVE List V5
Vulnerability Title
XmlNotepad 代码问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
XmlNotepad是Microsoft开源的一个XML文档浏览与编辑工具。 XmlNotepad 2.9.0.21之前版本存在代码问题漏洞，该漏洞源于默认未禁用DTD处理，可能导致解析恶意XML文件时泄露本地文件内容或凭据。
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
microsoft XmlNotepad < 2.9.0.21 -

II. Public POCs for CVE-2026-34401

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III. Intelligence Information for CVE-2026-34401

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Patches & Fixes for CVE-2026-34401 (2)

Vendor Advisories for CVE-2026-34401 (1)

Vendor Pages for CVE-2026-34401 (1)

IV. Related Vulnerabilities

Same vendor: microsoft
Same weakness: CWE-611

V. Comments for CVE-2026-34401

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