CVE-2026-34401

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.

• CWE-611

• https://github.com/microsoft/XmlNotepad/commit/3665603d61ba10b7827a3724e854748cb780140cPatch
• https://github.com/microsoft/XmlNotepad/commit/c03ab2311ac6960452eb1ab49098768f851dcc53Patch
• https://github.com/microsoft/XmlNotepad/releases/tag/2.9.0.21Product, Release Notes
• https://github.com/microsoft/XmlNotepad/security/advisories/GHSA-5j32-486h-42chMitigation, Vendor Advisory
• https://github.com/microsoft/XmlNotepad/security/advisories/GHSA-5j32-486h-42chMitigation, Vendor Advisory

Published

Mar 31, 2026

Last Modified

Jul 24, 2026

Status

Analyzed

• How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
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