CVE-2026-63119
MCP Ruby SDK: Unbounded line buffer in stdio transports leads to memory exhaustion (DoS)
CVSS Score
6.2
EPSS Score
0.0%
EPSS Percentile
0th
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.
| CWE | CWE-400 CWE-770 |
| Vendor | modelcontextprotocol |
| Product | ruby-sdk |
| Published | Jul 29, 2026 |
| Last Updated | Jul 29, 2026 |
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CVSS v3 Breakdown
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Attack Vector
Local
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High
Affected Versions
modelcontextprotocol / ruby-sdk
< 0.23.0