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EUVD-2026-290472

2026-10-05T14:01:52.617118+00:00

EUVD-2026-290472

fkie_cve-2026-40107

2026-10-05T14:01:52.617158+00:00

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.

GHSA-w95v-4h65-j455 — SiYuan Affected by Zero-Click NTLM Hash Theft and Blind SSRF via Mermaid Diagram Rendering

2026-10-05T14:01:52.617196+00:00

Affected: Go: github.com/siyuan-note/siyuan/kernel

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.

## Root Cause

Mermaid initialization at `app/src/protyle/render/mermaidRender.ts` lines 28 and 33:

mermaid.initialize({ securityLevel: "loose", flowchart: { htmlLabels: true, }, });

SVG injection at line 101:

renderElement.lastElementChild.innerHTML = mermaidData.svg;

No DOMPurify or other sanitization between the Mermaid output and DOM insertion.

Mermaid v11.12.0 in "loose" mode strips active JavaScript (`