Vulnerability · Published Apr 9, 2026 · Assigned by GitHub_M

CVE-2026-40107SiYuan Affected by Zero-Click NTLM Hash Theft and Blind SSRF via Mermaid Diagram Rendering

High 8.7

In plain English

A high-severity server-side request forgery in siyuan from siyuan-note. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 25% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)8.7High

Exploit odds (30 days)0.3%top 75.1% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official 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 packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Go	github.com/siyuan-note/siyuan/kernel	0.0.0-20260407035653-2f416e5253f1	GHSA-w95v-4h65-j455
Go	github.com/siyuan-note/siyuan/kernel	0.0.0-20260407035653-2f416e5253f1	GO-2026-5702

Affected products (as reported)

Vendor	Product	Versions
siyuan-note	siyuan	< 3.6.4

Weakness: CWE-918 · 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

References

https://github.com/siyuan-note/siyuan/security/advisories/GHSA-w95v-4h65-j455 x_refsource_CONFIRM