Threats affecting pkg:gem/mcp

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 reads and parses an entire JSON-RPC POST body without a size limit, allowing an unauthenticated remote attacker to exhaust process memory. This issue is fixed in version 0.23.0.

CVE-2026-67431 is a high-severity vulnerability in the MCP Ruby SDK prior to version 0.23.0. The issue involves improper access control where the StreamableHTTPTransport component does not bind session IDs to session owners. This flaw allows an attacker who has obtained a stolen session ID to send requests that execute within the victim's session context. The vulnerability is fixed in version 0.23.0.

MCP Ruby SDK is the official Ruby SDK for Model Context Protocol servers and clients. Prior to 0.23.0, MCP::Server::Transports::StdioTransport and MCP::Client::Stdio in the mcp gem use IO#gets without a byte limit, allowing a peer that sends data without a newline to exhaust process memory. This issue is fixed in version 0.23.0.

CVE-2026-67430 is a medium severity vulnerability in the MCP Ruby SDK prior to version 0.23.0. The issue involves the MCP::Server::Transports::StreamableHTTPTransport component not expiring sessions by default, causing unbounded retention of ServerSession objects. This can lead to memory exhaustion in the process due to repeated initialize requests. The vulnerability is fixed in version 0.23.0.

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 validate the HTTP Host or Origin request headers, which allows a malicious browser page to use DNS rebinding to reach a locally running MCP server and invoke exposed tools. This issue is fixed in version 0.23.0.