CVE-2026-40322: SiYuan: Mermaid `javascript:` Link Injection Leads to Stored XSS and Electron RCE

Severity: critical (CVSS 9.0 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: none known
Published: 2026-04-16 · updated 2026-06-17
Weakness: CWE-79

Description

SiYuan is an open-source personal knowledge management system. In versions 3.6.3 and below, Mermaid diagrams are rendered with securityLevel set to "loose", and the resulting SVG is injected into the DOM via innerHTML. This allows attacker-controlled javascript: URLs in Mermaid code blocks to survive into the rendered output. On desktop builds using Electron, windows are created with nodeIntegration enabled and contextIsolation disabled, escalating the stored XSS to arbitrary code execution when a victim opens a note containing a malicious Mermaid block and clicks the rendered diagram node. This issue has been fixed in version 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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