Which versions of Microsoft are affected by CVE-2026-40107?

SiYuan knowledge management system versions prior to 3.6.4 contain a critical vulnerability that allows unauthenticated attackers to harvest Windows NTLM credential hashes from users simply by…. A patch is available.

How to fix or mitigate CVE-2026-40107?

Within 24 hours: Inventory all SiYuan deployments and verify installed versions; disable Mermaid diagram rendering in SiYuan settings if available. Within 7 days: Implement network-level blocking of outbound SMB (port 445) and NetBIOS (ports 137-139) traffic from SiYuan client systems to untrusted networks; restrict SiYuan note sharing to verified internal users only; force password reset for all Windows domain accounts that may have accessed SiYuan notes. Within 30 days: Upgrade all SiYuan instances to version 3.6.4 or later once released by vendor; conduct credential audits and review authentication logs for suspicious SMB connection attempts from SiYuan client hosts.

Microsoft CVE-2026-40107

Q: What is the CVSS score of CVE-2026-40107?

CVE-2026-40107 has a CVSS 4.0 base score of 8.7 (High). CVSS vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X. EPSS exploitation probability: 0.1%.

EUVD-2026-21148 HIGH

Server-Side Request Forgery (SSRF) (CWE-918)

2026-04-09 security-advisories@github.com

GHSA-w95v-4h65-j455

SSRF Microsoft

8.7

CVSS 4.0 · GitHub Advisory

Severity by source

GitHub Advisory PRIMARY

8.7 HIGH

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Primary rating from GitHub Advisory · only source for this CVE.

CVSS VectorGitHub Advisory

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Lifecycle Timeline

Re-analysis Queued

Apr 16, 2026 - 20:37 vuln.today

cvss_changed

Patch released

Apr 10, 2026 - 20:30 nvd

Patch available

EUVD ID Assigned

Apr 09, 2026 - 21:22 euvd

EUVD-2026-21148

Analysis Generated

Apr 09, 2026 - 21:22 vuln.today

CVE Published

Apr 09, 2026 - 21:16 nvd

HIGH 8.7

DescriptionGitHub Advisory

SiYuan is a personal knowledge management system. Prior to 3.6.4, SiYuan configures Mermaid.js with securityLevel: "loose" and htmlLabels: true. In this mode, <img> tags with src attributes survive Mermaid's internal DOMPurify and land in SVG <foreignObject> blocks. The SVG is injected via innerHTML with no secondary sanitization. When a victim opens a note containing a malicious Mermaid diagram, the Electron client fetches the URL. On Windows, a protocol-relative URL (//attacker.com/image.png) resolves as a UNC path (\\attacker.com\image.png). Windows attempts SMB authentication automatically, sending the victim's NTLMv2 hash to the attacker. This vulnerability is fixed in 3.6.4.

AnalysisAI

NTLM credential theft in SiYuan personal knowledge management system (prior to 3.6.4) allows remote attackers to capture Windows user password hashes without authentication or user interaction. Misconfigured Mermaid.js rendering with securityLevel:loose permits unsanitized <img> tags within SVG foreignObject blocks. Protocol-relative URLs in malicious Mermaid diagrams trigger automatic SMB authentication on Windows, transmitting NTLMv2 hashes to attacker-controlled servers when victims open compromised notes. Electron client processes the SVG via innerHTML without secondary sanitization, enabling SSRF to UNC paths.

Technical ContextAI

Root cause combines CWE-918 SSRF with unsafe Mermaid.js configuration. securityLevel:loose bypasses DOMPurify restrictions; htmlLabels:true enables HTML injection in SVG foreignObject elements. innerHTML injection creates unvalidated network requests. Windows SMB auto-authentication converts protocol-relative URLs (//attacker.com) to UNC paths (\\attacker.com), forcing NTLM handshake without user prompt. CPE covers Electron-based desktop clients on all platforms (cpe:2.3:a:b3log:siyuan:*:*:*:*:*:*:*:*).

RemediationAI

Vendor-released patch: upgrade to SiYuan 3.6.4 immediately. Version 3.6.4 enforces stricter Mermaid.js securityLevel configuration and implements secondary sanitization of SVG content before DOM injection. Users unable to upgrade should disable Mermaid diagram rendering in application settings and avoid opening untrusted notes until patched. Windows environments face highest risk; consider network-level blocking of outbound SMB (ports 445, 139) to mitigate hash exfiltration. For technical details and vendor confirmation, review the official security advisory at https://github.com/siyuan-note/siyuan/security/advisories/GHSA-w95v-4h65-j455. No public exploit identified at time of analysis. Authentication requirement: unauthenticated (CVSS PR:N).