XML Notepad provides an interface for XML documents. Prior to version 2.9.0.21 it does not disable DTD processing by default, which allows external entities to be automatically resolved. An attacker can craft a malicious XML file containing a DTD that causes XML Notepad to make outbound HTTP or SMB requests, potentially leaking local file contents or capturing cached NTLM credentials. The vulnerability is classified under CWE‑611, exposing sensitive data.

The flaw affects Microsoft XML Notepad running on Windows platforms. Any installation of XML Notepad before version 2.9.0.21 is susceptible. The issue applies to the default configuration where DTD processing remains enabled.

The CVSS base score is 6.5, indicating moderate severity. EPSS shows a less than 1% chance of exploitation in the next year, and the flaw is not listed in the CISA KEV catalog. The likely attack vector is that a user must open a crafted XML file in XML Notepad; the vulnerability is local and does not require network access to the attacker. Exploitability is limited to contexts where the user has permission to access the file, but once triggered it can exfiltrate arbitrary file contents or capture session credentials.