CVE-2026-126393
Installing a SiYuan skill could make the server contact an internal service
SiYuan · MCP skill installer
First documented disclosure · Review checkpoint
Summary
The installer validated a download hostname before resolving the final network destination. The server could reach loopback services or internal metadata endpoints.
Severity and exploitation evidence
Medium · 5.3/10 · CVSS 4.0. Severity source.
Exploitation not established: The reviewed advisory does not report malicious exploitation.
Technical severity is not a measure of observed attacks or of risk to your deployment. Attempts, demonstrations, and successful compromise retain the qualifications in the source.
How the weakness works
The installer validated a download hostname before resolving the final network destination.
Conditions required
The MCP skill installation action processed a URL supplied by another party.
Potential impact
The server could reach loopback services or internal metadata endpoints.
Affected versions and configurations
Through 3.8.9.
Fix and mitigation status
3.8.10.
Practical next steps
Upgrade SiYuan to 3.8.10 or later and limit who may initiate skill installation.
Operating lesson
Apply outbound destination checks to each download and redirect.
Evidence and limits
The CVE record was published on 2026-11-13.
Sources
- Maintainer security advisory
Primary source ·
- VulnCheck CVE record
Primary source ·