Cyber Resilience

CVE-2026-34401

XXE in Microsoft Xml Notepad ≤ 2.9.0.21

XXE
Published
31 March 2026
Modified
24 July 2026
Patch / advisory
View advisory
CVSS Score v3.1 6.5
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
EPSS Score 0.0099 60th percentile
Risk Priority 52 floored blend · peak EPSS

CVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.

Summary

CVE-2026-34401 is a medium-severity Improper Restriction of XML External Entity Reference (CWE-611) vulnerability in Microsoft Xml Notepad. Its CVSS base score is 6.5 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked in the top 40% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to CM-6 (Configuration Settings) and SA-11 (Developer Testing and Evaluation) — see the control section below for these in your framework.

OWASP Top 10 for Web (2025)

A02:2025 Security Misconfiguration

EU & UK References

Vulnerability Data

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…

more

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.

CWE(s)
CWE-611

Related Threats

MITRE ATT&CK Enterprise Techniques

T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
T1005 Data from Local System Collection
Adversaries may search local system sources, such as file systems, configuration files, local databases, virtual machine files, or process memory, to find files of interest and sensitive data prior to Exfiltration.
attack.mitre.org →
T1213 Data from Information Repositories Collection
Adversaries may leverage information repositories to mine valuable information.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2024-30043Same vendor: Microsoft
CVE-2023-36419Same vendor: Microsoft
CVE-2024-49064Same vendor: Microsoft
CVE-2023-35389Same vendor: Microsoft
CVE-2023-22274Same vendor: Microsoft
CVE-2023-47160Same vendor: Microsoft
CVE-2026-57259Same vendor: Microsoft
CVE-2024-54171Same vendor: Microsoft
CVE-2024-49535Same vendor: Microsoft
CVE-2024-39726Same vendor: Microsoft

Affected Assets

microsoft
xml notepad
≤ 2.9.0.21

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V1.5.1
  • V15.3.2

Mitigating Controls (NIST 800-53 r5) AI

CM-6 Configuration Settings good match

Secure configuration settings can disable external entity processing in XML parsers.

SA-11 Developer Testing and Evaluation good match

Developer testing can discover XXE flaws through targeted XML parsing tests.

SI-10 Information Input Validation good match

Input validation can reject or sanitize XML containing external entity references.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-01 mostly match
prevents

Hardened XML parser configurations directly disable external entity resolution.

PR.PS-06 mostly match
prevents

Secure SDLC practices include input validation and safe XML parser configuration that prevent XXE.

ID.RA-01 partial match
prevents

Vulnerability scanning can discover XXE flaws but does not prevent their introduction in code.

PR.PS-02 partial match
prevents

Patching eliminates XXE-vulnerable parser versions but is only one aspect of software maintenance.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing in development catches XXE via static analysis and dynamic XML fuzzing.

A.8.8 Management of technical vulnerabilities mostly match
finds

Vulnerability management identifies and patches XML libraries with unsafe default entity settings.

A.8.25 Secure development life cycle partial match
prevents

Secure development life cycle mandates input validation and entity handling that directly prevents XXE.

A.8.26 Application security requirements partial match
prevents

Application security requirements explicitly call for disabling external entity processing in XML parsers.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure architecture principles include safe parser configuration that mitigates external entity risks.

A.8.28 Secure coding partial match
prevents

Secure coding standards require disabling DTDs and external entities in XML processing.

References