CVE-2026-34401XML Notepad: XML External Entity (XXE) Injection via Unsafe XmlTextReader in XML Diff and Schema Loading
Updated under an hour ago ()
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It affects microsoft XmlNotepad and 1 other product. Add what you run to find out whether that includes you.
No exploitation reported and no EPSS estimate yet.
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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.
- CVSS
- 6.5 MEDIUM (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
- Weakness (CWE)
- CWE-611
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- GitHub_M
- NVD analysis
- Analyzed
- Record last updated
- Apr 1, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
microsoft XmlNotepad microsoft:xmlnotepad (from the name) | before 2.9.0.21 | CNA record |
microsoft xml_notepad microsoft:xml_notepad | before 2.9.0.21 | NVD |
References
- https://github.com/microsoft/XmlNotepad/security/advisories/GHSA-5j32-486h-42chx-refsource-confirm, mitigation, vendor-advisory
- https://github.com/microsoft/XmlNotepad/commit/3665603d61ba10b7827a3724e854748cb780140cx-refsource-misc, patch
- https://github.com/microsoft/XmlNotepad/commit/c03ab2311ac6960452eb1ab49098768f851dcc53x-refsource-misc, patch
- https://github.com/microsoft/XmlNotepad/releases/tag/2.9.0.21x-refsource-misc, product, release-notes
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.