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 expi

mediumCVSS 5.3CVE-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.

Details

Source: NVD Recent CVEs (US · database · site)
Severity: medium — CVSS 5.3
Published: 2026-07-29
Last updated: 2026-07-30
Exploitation: Not in CISA KEV at last sync

Original advisory: https://nvd.nist.gov/vuln/detail/CVE-2026-67430

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-674300.29% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 21% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-67430	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

mediumGHSA-52jp-gj8w-j6xh: MCP Ruby SDK: Unbounded session retention in StreamableHTTPTransport allows memory exhaus…ghsa

Recent advisories for MCP Ruby SDK

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

highGHSA-5p9g-j988-pcwv: MCP Ruby SDK: Ruby SSE Session Poisoningghsa · 2026-07-30
highGHSA-h669-8m4g-r2hc: MCP Ruby SDK: Unbounded JSON-RPC request body causes uncontrolled memory allocation in St…ghsa · 2026-07-30
mediumGHSA-52jp-gj8w-j6xh: MCP Ruby SDK: Unbounded session retention in StreamableHTTPTransport allows memory exhaus…ghsa · 2026-07-30
mediumGHSA-7683-3w9x-ch42: MCP Ruby SDK: Unbounded line buffer in stdio transports leads to memory exhaustion (DoS)ghsa · 2026-07-30
mediumGHSA-rjr6-rcgv-9m7m: MCP Ruby SDK: Streamable HTTP transport lacks DNS-rebinding (Host/Origin) protectionghsa · 2026-07-30
highCVE-2026-67432: MCP Ruby SDK is the official Ruby SDK for Model Context Protocol servers and clients. Prior to…nvd · 2026-07-29