CVE-2026-34401: CWE-611: Improper Restriction of XML External Entity Reference in microsoft XmlNotepad
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.
AI Analysis
Technical Summary
Microsoft XmlNotepad versions before 2.9.0.21 improperly restrict XML external entity references (CWE-611) by not disabling DTD processing by default. This allows external entities in XML files to be resolved automatically, which can be exploited by attackers to trigger outbound network requests from the victim's machine. Such requests may lead to information disclosure, including local file contents or NTLM credential leakage. The vulnerability is addressed by disabling DTD processing by default starting with version 2.9.0.21.
Potential Impact
Successful exploitation can lead to disclosure of local files and NTLM credentials due to automatic resolution of external XML entities. This can compromise confidentiality but does not impact integrity or availability. The CVSS score is 6.5 (medium severity), reflecting network attack vector, low attack complexity, no privileges required, user interaction required, and high confidentiality impact.
Mitigation Recommendations
Upgrade Microsoft XmlNotepad to version 2.9.0.21 or later, where DTD processing is disabled by default, mitigating this vulnerability. No other mitigation is required as the issue is fixed in this official release.
CVE-2026-34401: CWE-611: Improper Restriction of XML External Entity Reference in microsoft XmlNotepad
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.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
Microsoft XmlNotepad versions before 2.9.0.21 improperly restrict XML external entity references (CWE-611) by not disabling DTD processing by default. This allows external entities in XML files to be resolved automatically, which can be exploited by attackers to trigger outbound network requests from the victim's machine. Such requests may lead to information disclosure, including local file contents or NTLM credential leakage. The vulnerability is addressed by disabling DTD processing by default starting with version 2.9.0.21.
Potential Impact
Successful exploitation can lead to disclosure of local files and NTLM credentials due to automatic resolution of external XML entities. This can compromise confidentiality but does not impact integrity or availability. The CVSS score is 6.5 (medium severity), reflecting network attack vector, low attack complexity, no privileges required, user interaction required, and high confidentiality impact.
Mitigation Recommendations
Upgrade Microsoft XmlNotepad to version 2.9.0.21 or later, where DTD processing is disabled by default, mitigating this vulnerability. No other mitigation is required as the issue is fixed in this official release.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-03-27T13:45:29.620Z
- Cvss Version
- 3.1
- State
- PUBLISHED
Threat ID: 69cc3b45e6bfc5ba1d430c9d
Added to database: 3/31/2026, 9:23:17 PM
Last enriched: 4/8/2026, 2:04:29 AM
Last updated: 5/15/2026, 9:51:25 AM
Views: 52
Community Reviews
0 reviewsCrowdsource mitigation strategies, share intel context, and vote on the most helpful responses. Sign in to add your voice and help keep defenders ahead.
Want to contribute mitigation steps or threat intel context? Sign in or create an account to join the community discussion.
Actions
Updates to AI analysis require Pro Console access. Upgrade inside Console → Billing.
Need more coverage?
Upgrade to Pro Console for AI refresh and higher limits.
For incident response and remediation, OffSeq services can help resolve threats faster.
Latest Threats
Check if your credentials are on the dark web
Instant breach scanning across billions of leaked records. Free tier available.