CVE-2026-63119— MCP Ruby SDK: Unbounded line buffer in stdio transports leads to memory exhaustion (DoS)
Possible ATT&CK Techniques 1AI
T1496 · Resource HijackingAffected Version Matrix 1
| Vendor | Product | Version Range | Status |
|---|---|---|---|
| modelcontextprotocol | ruby-sdk | < 0.23.0 | affected |
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I. Basic Information for CVE-2026-63119
Vulnerability Information
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Vulnerability Title
MCP Ruby SDK: Unbounded line buffer in stdio transports leads to memory exhaustion (DoS)
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
未加控制的资源消耗(资源穷尽)
Source: CVE Program / CVE List V5
Affected Products
| Vendor | Product | Affected Versions | CPE | Subscribe |
|---|---|---|---|---|
| modelcontextprotocol | ruby-sdk | < 0.23.0 | - |
II. Public POCs for CVE-2026-63119
| # | POC Description | Source Link | Shenlong Link |
|---|
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Patches & Fixes for CVE-2026-63119 (1)
Vendor Advisories for CVE-2026-63119 (1)
Vendor Pages for CVE-2026-63119 (1)
- 🔗 Release v0.23.0 · modelcontextprotocol/ruby-sdk · GitHubx_refsource_MISC
Same Patch Batch · modelcontextprotocol · 2026-07-29 · 5 CVEs total
| CVE-2026-67431 | 8.3 HIGH | MCP Ruby SDK: Ruby SSE Session Poisoning |
| CVE-2026-67432 | 7.5 HIGH | MCP Ruby SDK: Unbounded JSON-RPC request body causes uncontrolled memory allocation in Str |
| CVE-2026-63118 | 6.9 MEDIUM | MCP Ruby SDK: Streamable HTTP transport lacks DNS-rebinding (Host/Origin) protection |
| CVE-2026-67430 | 5.3 MEDIUM | MCP Ruby SDK: Unbounded session retention in StreamableHTTPTransport allows memory exhaust |
IV. Related Vulnerabilities
Same product: ruby-sdk
- CVE-2026-67432
MCP Ruby SDK: Unbounded JSON-RPC request body causes uncontr - CVE-2026-67431
MCP Ruby SDK: Ruby SSE Session Poisoning - CVE-2026-67430
MCP Ruby SDK: Unbounded session retention in StreamableHTTPT - CVE-2026-63118
MCP Ruby SDK: Streamable HTTP transport lacks DNS-rebinding - CVE-2026-33946
MCP Ruby SDK: Insufficient Session Binding Allows SSE Stream
Same vendor: modelcontextprotocol
- CVE-2026-67432
MCP Ruby SDK: Unbounded JSON-RPC request body causes uncontr - CVE-2026-67431
MCP Ruby SDK: Ruby SSE Session Poisoning - CVE-2026-67430
MCP Ruby SDK: Unbounded session retention in StreamableHTTPT - CVE-2026-63118
MCP Ruby SDK: Streamable HTTP transport lacks DNS-rebinding - CVE-2026-59950
MCP Python SDK: WebSocket server transport does not support
Same weakness: CWE-400
- CVE-2026-67437
OliveTin: Unauthenticated DoS via OAuth2 State Memory Exhaus - CVE-2026-58182
Apache Traffic Server: ts_lua plugin has initialization and - CVE-2026-65324
Apache Traffic Server: HTTP/2 and HTTP/3 dechunking removes - CVE-2026-58151
Apache Traffic Server: Abusive HTTP/2 framing can exhaust re - CVE-2026-59941
Dompdf: Uncontrolled resource consumption based on declared
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