CVE-2025-6515: Oatpp Oatpp-Mcp

Medium severity, CVSS 6.8. EPSS: 0.4% chance of exploitation in the next 30 days.

The MCP SSE endpoint in oatpp-mcp returns an instance pointer as the session ID, which is not unique nor cryptographically secure. This allows network attackers with access to the oatpp-mcp server to guess future session IDs and hijack legitimate client MCP sessions, returning malicious responses from the oatpp-mcp server.

Affected products

• Oatpp Oatpp-Mcp: version 0 only

Published 2025-10-20. Last modified 2026-10-08.