Mermaid

SiYuan is vulnerable to zero-click NTLM hash theft on Windows and blind SSRF on all platforms due to insecure Mermaid.js configuration, where a malicious Mermaid diagram containing a protocol-relative URL can be injected into a note, causing the Electron client to fetch the URL, triggering SMB authentication on Windows and sending the victim's NTLMv2 hash to the attacker. On macOS and Linux, the request acts as a tracking pixel and blind SSRF.

SiYuan versions 3.6.3 and below are vulnerable to arbitrary code execution due to insecure rendering of Mermaid diagrams, allowing injected javascript: URLs within Mermaid code blocks to execute arbitrary code when a victim opens a note containing a malicious Mermaid block and clicks the rendered diagram node.