CVE-2026-66012
Received Received - Intake

SiYuan Missing Authorization in MCP Endpoint

Publication date: 2026-07-25

Last updated on: 2026-07-25

Assigner: VulnCheck

Description
SiYuan before v3.7.2 contains a missing authorization vulnerability in the POST /mcp kernel endpoint, which is gated only by a general auth check (model.CheckAuth) with no admin-role or read-only enforcement. This exposes 31 MCP tools, including a file tool with list/read/write/delete/rename/copy actions across the entire workspace. When the Publish server is enabled in anonymous mode (Conf.Publish.Enable=true and Conf.Publish.Auth.Enable=false), the Publish reverse proxy attaches an anonymous RoleReader JWT to proxied requests, allowing a remote unauthenticated attacker to reach /mcp. The attacker can read conf/conf.json to extract accessAuthCode, api.token, and cookieKey in plaintext, write arbitrary files in the workspace, and plant a plugin into data/plugins/ that executes with nodeIntegration:true and no contextIsolation on the next desktop launch, leading to administrator takeover.

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Meta Information

Published
2026-07-25
Last Modified
2026-07-25
Generated
2026-07-25
AI Q&A
2026-07-25
EPSS Evaluated
N/A
NVD
CVE-2026-66012
EUVD
EUVD-2026-49043

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
siyuan siyuan to 3.7.2 (exc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-862 The product does not perform an authorization check when an actor attempts to access a resource or perform an action.

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Executive Summary

SiYuan before v3.7.2 has a missing authorization flaw in the POST /mcp kernel endpoint. It lacks admin-role or read-only enforcement, exposing 31 MCP tools including file operations. When the Publish server runs in anonymous mode, unauthenticated attackers can access /mcp via a RoleReader JWT. This allows reading sensitive files like conf.json, writing arbitrary files, and planting malicious plugins that execute with high privileges on the next desktop launch.

Impact Analysis

An attacker could read sensitive data like accessAuthCode, api.token, and cookieKey from conf.json. They may write arbitrary files in the workspace, including malicious plugins. These plugins execute with administrator privileges and no isolation, leading to full system compromise. All data and system integrity are at risk.

Compliance Impact

This vulnerability likely violates GDPR and HIPAA due to unauthorized access to sensitive data (confidentiality breach) and potential data exfiltration or tampering (integrity breach). It enables full system compromise, risking unauthorized disclosure of personal or health data, which is non-compliant with strict access control and data protection requirements.

Mitigation Strategies

Upgrade SiYuan to v3.7.2 or later to address the missing authorization vulnerability in the /mcp endpoint. Disable the Publish server in anonymous mode by setting Conf.Publish.Enable=false or enabling authentication with Conf.Publish.Auth.Enable=true. Review and restrict file permissions in the workspace to limit unauthorized access.

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