CVE-2026-67430Public exploitNetwork attack vector

Memory exhaustion via unbounded session retention

Published Jul 29, 2026 · Updated Jul 29, 2026

Denial of service in MCP Ruby SDK before 0.23.0 allows remote attackers to exhaust server memory through repeated initialize requests. StreamableHTTPTransport defaults to no idle timeout, stores each successful initialization as a ServerSession under a fresh UUID, and removes it only after a client DELETE or stream error. Exploitation requires unauthenticated TCP access to a stateful MCP HTTP endpoint; stateless deployments do not retain sessions.

CVSS severity5.3
Medium
EPSS probability0.31%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Denial of service in MCP Ruby SDK before 0.23.0 allows remote attackers to exhaust server memory through repeated initialize requests. StreamableHTTPTransport defaults to no idle timeout, stores each successful initialization as a ServerSession under a fresh UUID, and removes it only after a client DELETE or stream error. Exploitation requires unauthenticated TCP access to a stateful MCP HTTP endpoint; stateless deployments do not retain sessions.

The record

CVE
CVE-2026-67430
Published
Jul 29, 2026
Updated
Jul 29, 2026
Vendor
Model Context Protocol
Product
MCP Ruby SDK
Classifications
CWE-401, CWE-770, T1499.003
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 29, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 29, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 0.23.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Model Context Protocol · MCP Ruby SDKversion=< 0.23.0

Published CVSS scores

5.3GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-401Missing Release of Memory after Effective Lifetime
CWE-770Allocation of Resources Without Limits or Throttling
T1499.003Application Exhaustion Flood

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo