Vulnerability · Published Jul 29, 2026 · Assigned by GitHub_M

CVE-2026-67432MCP Ruby SDK: Unbounded JSON-RPC request body causes uncontrolled memory allocation in StreamableHTTPTransport

High 7.5

In plain English

A high-severity resource allocation without limits in ruby-sdk from modelcontextprotocol. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.8% (higher than 56% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.5High

Exploit odds (30 days)0.8%top 43.8% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
RubyGems	mcp	0.23.0	GHSA-h669-8m4g-r2hc

Affected products (as reported)

Vendor	Product	Versions
modelcontextprotocol	ruby-sdk	< 0.23.0

Weakness: CWE-770 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-h669-8m4g-r2hc x_refsource_CONFIRM
https://github.com/modelcontextprotocol/ruby-sdk/commit/772e0cb1f9db69312006926eee59a7287ad50166 x_refsource_MISC
https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.23.0 x_refsource_MISC