CVE-2026-67430

Medium

Description

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 expire sessions by default, so repeated initialize requests retain unbounded ServerSession objects and can exhaust process memory. This issue is fixed in version 0.23.0.

SeverityMedium

CVSS5.3

Exploit probability31. percentile0.4%

ProductModelcontextprotocol Ruby-sdk

PublishedJul 29, 2026

First seenJul 29, 2026

Weakness typeCWE-401CWE-401 CWE-770Allocation of resources without limits

How to fix

Sources list no fixed version or patch link for this vulnerability.

Affected products

Product	Affected versions	Fixed in
modelcontextprotocol ruby-sdk	< 0.23.0	—

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