XML Notepad: XML External Entity (XXE) Injection via Unsafe XmlTextReader in XML Diff and Schema Loading

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Summary

CVECVE-2026-34401
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-03-31 22:16:18 UTC
Updated2026-04-01 17:28:40 UTC
DescriptionXML 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.

Risk And Classification

Primary CVSS: v3.1 6.5 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N

EPSS: 0.002240000 probability, percentile 0.450230000 (date 2026-04-01)

Problem Types: CWE-611 | CWE-611 CWE-611: Improper Restriction of XML External Entity Reference

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary6.5MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
3.1CNADECLARED6.5MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Microsoft XmlNotepad affected < 2.9.0.21 Not specified

References

ReferenceSourceLinkTags
github.com/microsoft/XmlNotepad/security/advisories/GHSA-5j32-486h-42ch 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
github.com/microsoft/XmlNotepad/commit/3665603d61ba10b7827a3724e854748cb... [email protected] github.com
github.com/microsoft/XmlNotepad/commit/c03ab2311ac6960452eb1ab49098768f8... [email protected] github.com
github.com/microsoft/XmlNotepad/releases/tag/2.9.0.21 [email protected] github.com
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