Resource exhaustion in Modelcontextprotocol Ruby-Sdk

CVE-2026-67430

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.

Published · last modified .

CVSS v3 metric

CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L.

EPSS exploit prediction

EPSS: 0.004 (30.8th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 31st percentile — 30.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-67430: held from 0.005 to 0.004.

EPSS over last 30 days · oldest: 0.005 · newest: 0.004 · change: -0.001

Affected products

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-67430?
CVE-2026-67430 is a medium-severity vulnerability in Modelcontextprotocol Ruby-Sdk, classified under Missing Release of Memory after Effective Lifetime. CVSS score: 5.3/10. Published 2026-07-29.
How severe is CVE-2026-67430?
Medium severity. CVSS v3 base score is 5.3 out of 10.