What’s Vulnerable › Vulnerabilities
CVE-2026-40107: SiYuan Affected by Zero-Click NTLM Hash Theft and Blind SSRF via Mermaid Diagram Rendering
- Severity: medium (CVSS 6.5 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.3% probability of exploitation in the next 30 days
- Public exploit or detection template: yes
- Published: 2026-04-09 · updated 2026-06-17
- Weakness: CWE-918
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, <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.
Affected products
- siyuan-note siyuan: before 3.6.4 — fixed in 3.6.4
How to fix
Upgrade to a fixed version: siyuan-note siyuan 3.6.4. Check the vendor advisory for mitigations.
References
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