medium6.2
CVE-2026-63119
MCP Ruby SDK: Unbounded line buffer in stdio transports leads to memory exhaustion (DoS)
Impact
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 packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| rubygems | mcp | <= 0.22.0 | 0.23.0 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-7683-3w9x-ch42
- https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-7683-3w9x-ch42
- https://nvd.nist.gov/vuln/detail/CVE-2026-63119
- https://github.com/modelcontextprotocol/ruby-sdk/commit/267b8fa6285453525c81ce43db6b7dcd7a8a8c2f
- https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.23.0