CVE-2026-67430: medium-severity vulnerability in modelcontextprotocol ruby-sdk
MCP Ruby SDK: Unbounded session retention in StreamableHTTPTransport allows memory exhaustion via initialize flood
Published · Updated
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13Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 5.3epss 0.4%
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.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Affected products
modelcontextprotocol · ruby-sdkRelated CVEs — modelcontextprotocol ruby-sdk
In the same product, most dangerous first.
CVE-2026-67432HIGHMCP Ruby SDK: Unbounded JSON-RPC request body causes uncontrolled memory allocation in StreamableHTTPTransportEPSS 0.8%CVE-2026-33946HIGHMCP Ruby SDK: Insufficient Session Binding Allows SSE Stream Hijacking via Session ID ReplayEPSS 0.5%CVE-2026-67431HIGHMCP Ruby SDK: Ruby SSE Session PoisoningEPSS 0.4%CVE-2026-63118MEDIUMMCP Ruby SDK: Streamable HTTP transport lacks DNS-rebinding (Host/Origin) protectionEPSS 0.2%CVE-2026-63119MEDIUMMCP Ruby SDK: Unbounded line buffer in stdio transports leads to memory exhaustion (DoS)EPSS 0.2%