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 reads and parses an entire JSON-RPC POST body without a size limit, allowing an unauthenticated remote attacker to exhaust process memory. This issue is fixed in version 0.23.0.
Published: 2026-07-29
Score: 7.5 High
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
AI Analysis

Impact

The MCP Ruby SDK allows an unlimited JSON‑RPC POST body to be read and parsed by the StreamableHTTPTransport component before version 0.23.0. Because no size limit is enforced, an attacker can send an excessively large request that consumes available process memory, potentially causing the application to crash or become unresponsive. This constitutes an uncontrolled memory allocation flaw identified as CWE-770.

Affected Systems

The vulnerable component is part of the Model Context Protocol Ruby SDK (vendor modelcontextprotocol). Versions prior to 0.23.0 are affected; the issue was fixed in release v0.23.0.

Risk and Exploitability

The vulnerability carries a CVSS score of 7.5, indicating high severity. The EPSS score is below 1%, suggesting a low current exploitation probability, and it is not listed in the CISA KEV catalog. The likely attack vector is a remote unauthenticated attacker sending an excessively large JSON‑RPC request over HTTP. The unbounded request causes uncontrolled memory allocation, which can exhaust process memory and potentially crash or render the application unresponsive.

Generated by OpenCVE AI on August 2, 2026 at 07:41 UTC.

Remediation

No vendor fix or workaround currently provided.

OpenCVE Recommended Actions

  • Upgrade the MCP Ruby SDK to version 0.23.0 or later, which implements a size limit on JSON‑RPC requests.
  • If an upgrade is not feasible immediately, configure a reverse proxy or network firewall rule to limit the size of incoming POST payloads to a safe threshold.
  • Monitor process memory usage and configure alerts to detect anomalous consumption that may indicate an attempted exploitation.

Generated by OpenCVE AI on August 2, 2026 at 07:41 UTC.

Tracking

Sign in to view the affected projects.

Advisories
Source ID Title
Github GHSA Github GHSA GHSA-h669-8m4g-r2hc MCP Ruby SDK: Unbounded JSON-RPC request body causes uncontrolled memory allocation in StreamableHTTPTransport
History

Wed, 29 Jul 2026 21:00:00 +0000

Type Values Removed Values Added
First Time appeared Modelcontextprotocol
Modelcontextprotocol ruby-sdk
Vendors & Products Modelcontextprotocol
Modelcontextprotocol ruby-sdk

Wed, 29 Jul 2026 20:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Wed, 29 Jul 2026 19:30:00 +0000

Type Values Removed Values Added
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 reads and parses an entire JSON-RPC POST body without a size limit, allowing an unauthenticated remote attacker to exhaust process memory. This issue is fixed in version 0.23.0.
Title MCP Ruby SDK: Unbounded JSON-RPC request body causes uncontrolled memory allocation in StreamableHTTPTransport
Weaknesses CWE-770
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}

Subscriptions

Modelcontextprotocol Ruby-sdk
cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-07-29T19:34:24.640Z

Reserved: 2026-07-29T15:07:24.991Z

Link: CVE-2026-67432

cve-icon Vulnrichment

Updated: 2026-07-29T19:34:18.482Z

cve-icon NVD

Status : Deferred

Published: 2026-07-29T20:17:12.277

Modified: 2026-07-30T19:30:33.710

Link: CVE-2026-67432

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-08-02T07:45:03Z

Weaknesses
  • CWE-770

    Allocation of Resources Without Limits or Throttling