CVE-2026-67430: Modelcontextprotocol Ruby-SDK

Medium severity, CVSS 5.3. 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 0.23.0, MCP::Server::Transports::StreamableHTTPTransport in the mcp gem does not expire sessions by default, so repeated initialize requests retain unbounded ServerSession objects and can exhaust process memory. This issue is fixed in version 0.23.0.

Affected products

• Modelcontextprotocol Ruby-SDK: before 0.23.0 (fixed in 0.23.0)

Published 2026-07-29. Last modified 2026-07-30.