XXE in Microsoft XML Notepad
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.
Vulnerability class: XXE (XML External Entity)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N.
EPSS exploit prediction
EPSS: 0.014 (71.3th percentile), scored .
Low probability of exploitation in the next 30 days, but still tracked. 71st percentile — 71.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.010 · newest: 0.014 · change: +0.004
Affected products
- Microsoft XML Notepad
- Microsoft Xmlnotepad — versions < 2.9.0.21
Weakness classification (CWE)
References
- github.com/microsoft/XmlNotepad/security/advisories/GHSA-5j32-486h-42ch (Mitigation, Vendor Advisory)
- github.com/microsoft/XmlNotepad/commit/3665603d61ba10b7827a3724e854748cb780140c (Patch)
- github.com/microsoft/XmlNotepad/commit/c03ab2311ac6960452eb1ab49098768f851dcc53 (Patch)
- github.com/microsoft/XmlNotepad/releases/tag/2.9.0.21 (Product, Release Notes)
Frequently asked questions
- What is CVE-2026-34401?
- CVE-2026-34401 is a medium-severity vulnerability in Microsoft XML Notepad, classified under Improper Restriction of XML External Entity Reference (XXE). CVSS score: 6.5/10. Published 2026-03-31.
- How severe is CVE-2026-34401?
- Medium severity. CVSS v3 base score is 6.5 out of 10.