CVE-2026-59809: Siyuan-Note Siyuan

Medium severity, CVSS 4.9. EPSS: 0.4% chance of exploitation in the next 30 days.

SiYuan before v3.8.0 interpolates secret placeholders into the destination URL parameter of the http_request MCP tool, allowing attackers to exfiltrate stored secrets. An MCP client can craft a request with an attacker-controlled URL containing secret placeholders to send plaintext secret values to any public host without confirmation.

Affected products

• Siyuan-Note Siyuan: before 3.8.0 (fixed in 3.8.0)

Published 2026-08-22. Last modified 2026-08-26.