Critical Zero-Day Vulnerability in SiYuan Exposes Sensitive Data and Enables Remote Code Execution

Overview

CVE-2026-66012, a CVSS-10.0 vulnerability in SiYuan, allows unauthenticated attackers to bypass authorization and perform arbitrary file operations, including data exfiltration and plugin execution. This flaw poses severe risks to organizations using SiYuan, particularly Defense Industrial Base (DIB) and enterprise environments.

Technical Analysis

The vulnerability stems from a missing admin-role enforcement in the POST /mcp endpoint, accessible via the Publish server in anonymous mode. When Conf.Publish.Auth.Enable is false, the reverse proxy appends a RoleReader JWT to unauthenticated requests. This enables attackers to read/write/delete workspace files, extract plaintext credentials (accessAuthCode, api.token, cookieKey), and deploy malicious plugins with node-level execution privileges. Exploitation requires no credentials and can be triggered via simple HTTP requests to the /mcp endpoint.

Enterprise & DIB Impact

DIB and enterprises leveraging SiYuan for sensitive documentation or collaboration face immediate risks of intellectual property theft, sabotage, or persistent access. Attackers could alter mission-critical data, inject malicious code into workflows, or disrupt operations by tampering with published content or internal tools.

Recommended Actions

• 1. Upgrade to SiYuan v3.7.2 immediately to patch the flaw
• 2. Disable anonymous Publish mode by setting Conf.Publish.Auth.Enable=true
• 3. Validate JWT role enforcement in custom reverse-proxy configurations
• 4. Restrict network access to SiYuan instances using firewalls
• 5. Monitor logs for anomalous /mcp requests and investigate unauthenticated activity.