High severityNVD Advisory· Published Jul 29, 2026· Updated Jul 29, 2026
MCP Ruby SDK: Unbounded JSON-RPC request body causes uncontrolled memory allocation in StreamableHTTPTransport
CVE-2026-67432
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
Versions sourced from the GitHub Security Advisory.
| Package | Affected versions | Patched versions |
|---|---|---|
mcpRubyGems | < 0.23.0 | 0.23.0 |
Affected products
1- Range: <0.23.0
Patches
Vulnerability mechanics
References
5- github.com/advisories/GHSA-h669-8m4g-r2hcghsaADVISORY
- nvd.nist.gov/vuln/detail/CVE-2026-67432ghsaADVISORY
- github.com/modelcontextprotocol/ruby-sdk/commit/772e0cb1f9db69312006926eee59a7287ad50166ghsax_refsource_MISCWEB
- github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.23.0ghsax_refsource_MISCWEB
- github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-h669-8m4g-r2hcghsax_refsource_CONFIRMWEB
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