GHSA-RJR6-RCGV-9M7M MCP Ruby SDK: Streamable HTTP transport lacks DNS-rebinding (Host/Origin) protection

Summary MCP::Server::Transports::StreamableHTTPTransport the Rack-mountable Streamable HTTP transport in the mcp gem processes every incoming JSON-RPC request without ever inspecting the HTTP Host or Origin request headers. There is no AllowedHosts/AllowedOrigins allowlist and no DNS-rebinding...