MCP Ruby SDK: Unbounded session retention in StreamableHTTPTransport allows memory exhaustion via initialize flood

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-67430
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-29 20:17:11 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 does not expire sessions by default, so repeated initialize requests retain unbounded ServerSession objects and can exhaust process memory. This issue is fixed in version 0.23.0.

Risk And Classification

Primary CVSS: v3.1 5.3 MEDIUM from [email protected]

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

EPSS: 0.002910000 probability, percentile 0.214150000 (date 2026-07-31)

Problem Types: CWE-401 | CWE-770 | CWE-401 CWE-401: Missing Release of Memory after Effective Lifetime | CWE-770 CWE-770: Allocation of Resources Without Limits or Throttling

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary5.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
3.1CNADECLARED5.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS v3.1 Breakdown

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

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

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/commit/afb968c468c178c4d3294b42... [email protected] github.com
github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-52jp-g... 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
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