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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-67432
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-29 20:17:12 UTC
Updated2026-07-30 19:30:33 UTC
DescriptionMCP 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.

Risk And Classification

Primary CVSS: v3.1 7.5 HIGH from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS: 0.004360000 probability, percentile 0.358930000 (date 2026-07-31)

Problem Types: CWE-770 | CWE-770 CWE-770: Allocation of Resources Without Limits or Throttling

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
3.1CNADECLARED7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Modelcontextprotocol Ruby-sdk affected < 0.23.0 Not specified

References

ReferenceSourceLinkTags
github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.23.0 [email protected] github.com
github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-h669-8... 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
github.com/modelcontextprotocol/ruby-sdk/commit/772e0cb1f9db69312006926e... [email protected] github.com
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