CVE-2026-63119

MCP Ruby SDK: Unbounded line buffer in stdio transports leads to memory exhaustion (DoS)

State: Published
Severity: 6.2 Medium
Published: Jul 29, 2026
Updated: Jul 29, 2026
Reserved: Jul 15, 2026

Description

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.

Scores

CVSS	Score	Vector	Source
3.1	6.2 Medium	CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H	GitHub_M

Weaknesses

CWE-400 Uncontrolled Resource Consumption
CWE-770 Allocation of Resources Without Limits or Throttling

Affected Products

Product	Versions
ruby-sdkmodelcontextprotocol	< 0.23.0Affected

References

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