Vulnerability · Published Mar 31, 2026 · Assigned by GitHub_M
CVE-2026-34401XML Notepad: XML External Entity (XXE) Injection via Unsafe XmlTextReader in XML Diff and Schema Loading
Medium 6.5
In plain English
A medium-severity XML external entity in XmlNotepad from microsoft. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 1.0% (higher than 64% of all known vulnerabilities).
Official 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.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| microsoft | XmlNotepad | < 2.9.0.21 |
Weakness: CWE-611 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
References
- https://github.com/microsoft/XmlNotepad/security/advisories/GHSA-5j32-486h-42ch x_refsource_CONFIRM
- https://github.com/microsoft/XmlNotepad/commit/3665603d61ba10b7827a3724e854748cb780140c x_refsource_MISC
- https://github.com/microsoft/XmlNotepad/commit/c03ab2311ac6960452eb1ab49098768f851dcc53 x_refsource_MISC
- https://github.com/microsoft/XmlNotepad/releases/tag/2.9.0.21 x_refsource_MISC