CVE-2026-67432: Model Context Protocol Ruby SDK memory exhaustion in StreamableHTTPTransport

CVE-2026-67432 · Severity: high · CVSS 7.5 · Published 2026-07-29

The Model Context Protocol (MCP) Ruby SDK is a library used to build servers that connect AI models with local tools and data. A vulnerability in how the server handles incoming web requests allows an unauthenticated attacker to crash the server by sending a single, specially crafted large message. This results in a denial of service, making the AI tools and integrated services unavailable to legitimate users.

Technologies: Anthropic Model Context Protocol, mcp (RubyGems). Vendors: Anthropic, RubyGems.

Quick answers

Is CVE-2026-67432 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-67432 being exploited in the wild.
How severe is CVE-2026-67432?
High severity, with a CVSS score of 7.5, published 29 July 2026.
Which products and versions are affected?
Anthropic Model Context Protocol <= 0.22.0; mcp (RubyGems) ECOSYSTEM:introduced=0,fixed=0.23.0.
Is there a fix for CVE-2026-67432?
Yes. mcp (RubyGems): upgrade to 0.23.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-67432 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-67432?
Check whether you run Anthropic Model Context Protocol or mcp (RubyGems) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • mcp (RubyGems): upgrade to 0.23.0 or later
    bundle update mcp

Technical details

A resource exhaustion vulnerability (CWE-770) exists in the `StreamableHTTPTransport` and `StdioTransport` components of the MCP Ruby SDK. The `handle_post` method in the HTTP transport reads the entire request body into memory using `request.body.read` without enforcing a size limit or checking the `Content-Length` header. Subsequently, `JSON.parse` is called on the unbounded string, leading to massive memory allocation and potential Out-Of-Memory (OOM) termination of the worker process. This occurs before any session validation or authentication, allowing unauthenticated network-based exploitation. The issue is addressed in version 0.23.0 by implementing request size limits.

Affected products

  • Model Context Protocol (MCP) mcp <= 0.22.0

Identifiers

  • CVE-2026-67432
  • GHSA-h669-8m4g-r2hc

Timeline

  • 2026-07-08: disclosed
  • 2026-07-29: advisory: NVD publication date
  • 2026-07-30: patched: GitHub Advisory published and version 0.23.0 released

References

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