CVE-2026-33946: Lfprojects Mcp Ruby SDK

Medium severity, CVSS 5.9. EPSS: 0.5% chance of exploitation in the next 30 days.

MCP Ruby SDK is the official Ruby SDK for Model Context Protocol servers and clients. Prior to version 0.9.2, the Ruby SDK's streamable_http_transport.rb implementation contains a session hijacking vulnerability. An attacker who obtains a valid session ID can completely hijack the victim's Server-Sent Events (SSE) stream and intercept all real-time data. Version 0.9.2 contains a patch.

Affected products

• Lfprojects Mcp Ruby SDK: before 0.9.2 (fixed in 0.9.2)

Published 2026-03-27. Last modified 2026-06-17.