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

Source: https://junglewise.ai/threats/cve-2026-67432-model-context-protocol-ruby-sdk-memory-exhaustion-in  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-29. Updated: 2026-07-30  
License: CC BY 4.0 with a link back

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](https://junglewise.ai/threats/technologies/model-context-protocol), [mcp (RubyGems)](https://junglewise.ai/threats/technologies/rubygems-mcp). Vendors: [Anthropic](https://junglewise.ai/threats/vendors/anthropic), [RubyGems](https://junglewise.ai/threats/vendors/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

  ```sh
  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

- [https://api.github.com/users/hewei-gikaku](https://api.github.com/users/hewei-gikaku)
- [https://github.com/hewei-gikaku](https://github.com/hewei-gikaku)
- [https://api.github.com/users/hewei-gikaku/gists%7B/gist_id%7D](https://api.github.com/users/hewei-gikaku/gists%7B/gist_id%7D)
- [https://api.github.com/users/hewei-gikaku/repos](https://api.github.com/users/hewei-gikaku/repos)
- [https://avatars.githubusercontent.com/u/277980086?v=4](https://avatars.githubusercontent.com/u/277980086?v=4)
- [https://api.github.com/users/hewei-gikaku/events%7B/privacy%7D](https://api.github.com/users/hewei-gikaku/events%7B/privacy%7D)

## Related threats

- [RMCP Streamable HTTP server unauthenticated session-table memory leak](https://junglewise.ai/threats/cve-2026-63128-rmcp-streamable-http-server-unauthenticated-session-table-memory)
- [RMCP missing resource field validation in OAuth metadata](https://junglewise.ai/threats/cve-2026-63127-rmcp-missing-resource-field-validation-in-oauth-metadata)
- [modelcontextprotocol ruby-sdk session hijacking in StreamableHTTPTransport](https://junglewise.ai/threats/cve-2026-67431-modelcontextprotocol-ruby-sdk-session-hijacking-in)
- [Model Context Protocol Ruby SDK memory exhaustion in StreamableHTTPTransport](https://junglewise.ai/threats/cve-2026-67430-model-context-protocol-ruby-sdk-memory-exhaustion-in)
- [modelcontextprotocol ruby-sdk memory exhaustion in Stdio transports](https://junglewise.ai/threats/cve-2026-63119-modelcontextprotocol-ruby-sdk-memory-exhaustion-in-stdio)