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CVE-2026-63119

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

Published: Jul 29, 2026Updated: Jul 30, 2026 Sources: CVE List NVDCWE-400
6.2MEDIUM
NVD MITRE
EPSS Score
0.1%
Top 97.1%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
No Fix Available
Self-Check
Not available

Description

MCP 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.

No summary for this CVE yet.

CVSS Vector Breakdown

AV:LAC:LPR:NUI:NS:UC:NI:NA:H
Exploitability
AV:LAttack Vector
Local
AC:LAttack Complexity
Low
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:NConfidentiality
None
I:NIntegrity
None
A:HAvailability
High
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Weaknesses

CWE-400CWE-770

Affected Products

modelcontextprotocol
oss-projectaka model context protocol, mcp
ruby-sdkMixed
AI / ML / ai-agent-tooling

Exploitability

No known exploits, KEV entries, or remediation guidance available for this vulnerability yet.

Attack Graph

Products CVE Techniques Tactics

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MITRE ATT&CK

1 technique
Impact
View detailed technique mapping

References

https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-7683-3w9x-ch42
github.com
https://github.com/modelcontextprotocol/ruby-sdk/commit/267b8fa6285453525c81ce43db6b7dcd7a8a8c2f
github.com
https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.23.0
github.com

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