CVE-2026-63119: Modelcontextprotocol Ruby-SDK

Medium severity, CVSS 6.2. EPSS: 0.2% 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::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.

Affected products

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

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