CVE-2026-40107
Severity CVSS v4.0:
HIGH
Type:
CWE-918
Server-Side Request Forgery (SSRF)
Publication date:
09/04/2026
Last modified:
09/04/2026
Description
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, tags with src attributes survive Mermaid's internal DOMPurify and land in SVG 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.
Impact
Base Score 4.0
8.70
Severity 4.0
HIGH