CVE-2026-34401 | Microsoft XmlNotepad prior 2.9.0.21 HTTP/SMB xml external entity reference (GHSA-5j32-486h-42ch)

VDB-354585 · CVE-2026-34401 · GHSA-5J32-486H-42CH MICROSOFT XMLNOTEPAD PRIOR 2.9.0.21 HTTP/SMB XML EXTERNAL ENTITY REFERENCE HISTORYDIFFRELATEJSONXMLCTI CVSS Meta Temp Score Current Exploit Price (≈) CTI Interest Score 6.2 $0-$5k 1.65+ Summaryinfo A vulnerability was found in Microsoft XmlNotepad. It has been rated as problematic. Affected by this vulnerability is an unknown functionality of the component HTTP/SMB. Performing a manipulation results in xml external entity reference. This vulnerability is known as CVE-2026-34401. Remote exploitation of the attack is possible. No exploit is available. Upgrading the affected component is advised. Detailsinfo A vulnerability, which was classified as critical, was found in Microsoft XmlNotepad. This affects an unknown function of the component HTTP/SMB. The manipulation with an unknown input leads to a xml external entity reference vulnerability. CWE is classifying the issue as CWE-611. The product processes an XML document that can contain XML entities with URIs that resolve to documents outside of the intended sphere of control, causing the product to embed incorrect documents into its output. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is: 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. The advisory is shared at github.com. This vulnerability is uniquely identified as CVE-2026-34401 since 03/27/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. It demands that the victim is doing some kind of user interaction. Neither technical details nor an exploit are publicly available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 04/01/2026). Upgrading to version 2.9.0.21 eliminates this vulnerability. The upgrade is hosted for download at github.com. Applying the patch 3665603d61ba10b7827a3724e854748cb780140c is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version. Productinfo Vendor Microsoft Name XmlNotepad License commercial Website Vendor: https://www.microsoft.com/ Product: https://github.com/microsoft/XmlNotepad/ CPE 2.3info 🔒 CPE 2.2info 🔒 CVSSv4info VulDB Vector: 🔒 VulDB Reliability: 🔍 CVSSv3info VulDB Meta Base Score: 6.4 VulDB Meta Temp Score: 6.2 VulDB Base Score: 6.3 VulDB Temp Score: 6.0 VulDB Vector: 🔒 VulDB Reliability: 🔍 CNA Base Score: 6.5 CNA Vector (GitHub_M): 🔒 CVSSv2info Vector Complexity Authentication Confidentiality Integrity Availability Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock VulDB Base Score: 🔒 VulDB Temp Score: 🔒 VulDB Reliability: 🔍 Exploitinginfo Class: Xml external entity reference CWE: CWE-611 / CWE-610 CAPEC: 🔒 ATT&CK: 🔒 Physical: No Local: No Remote: Yes Availability: 🔒 Status: Not defined Price Prediction: 🔍 Current Price Estimation: 🔒 0-Day Unlock Unlock Unlock Unlock Today Unlock Unlock Unlock Unlock Threat Intelligenceinfo Interest: 🔍 Active Actors: 🔍 Active APT Groups: 🔍 Countermeasuresinfo Recommended: Upgrade Status: 🔍 0-Day Time: 🔒 Upgrade: XmlNotepad 2.9.0.21 Patch: 3665603d61ba10b7827a3724e854748cb780140c Timelineinfo 03/27/2026 CVE reserved 04/01/2026 +4 days Advisory disclosed 04/01/2026 +0 days VulDB entry created 04/01/2026 +0 days VulDB entry last update Sourcesinfo Vendor: microsoft.com Product: github.com Advisory: GHSA-5j32-486h-42ch Status: Confirmed CVE: CVE-2026-34401 (🔒) GCVE (CVE): GCVE-0-2026-34401 GCVE (VulDB): GCVE-100-354585 Entryinfo Created: 04/01/2026 04:39 Changes: 04/01/2026 04:39 (67) Complete: 🔍 Cache ID: 99:2DF:101 Discussion No comments yet. Languages: en. Please log in to comment. ◂ PreviousOverviewNext ▸