MCP Ruby SDK: Unbounded line buffer in stdio transports leads to memory exhaustion (DoS)

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-63119
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-29 20:17:10 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::StdioTransport and MCP::Client::Stdio in the mcp gem use IO#gets without a byte limit, allowing a peer that sends data without a newline to exhaust process memory. This issue is fixed in version 0.23.0.

Risk And Classification

Primary CVSS: v3.1 6.2 MEDIUM from [email protected]

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

EPSS: 0.001290000 probability, percentile 0.029490000 (date 2026-08-01)

Problem Types: CWE-400 | CWE-770 | CWE-400 CWE-400: Uncontrolled Resource Consumption | CWE-770 CWE-770: Allocation of Resources Without Limits or Throttling

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary6.2MEDIUMCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
3.1CNADECLARED6.2MEDIUMCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS v3.1 Breakdown

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

CVSS:3.1/AV:L/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/commit/267b8fa6285453525c81ce43... [email protected] github.com
github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-7683-3... 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
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NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

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