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CVE-2026-63119— MCP Ruby SDK: Unbounded line buffer in stdio transports leads to memory exhaustion (DoS)

Quick assessment

Affected
modelcontextprotocol ruby-sdk
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Model Context Protocol MCP Ruby SDK是Model Context Protocol组织的一个Ruby软件开发工具包组件。 Model Context Protocol MCP Ruby SDK 0.23.0之前版本存在资源管理错误漏洞，该漏洞源于使用IO#gets时未限制字节数，允许对等端发送无换行数据耗尽进程内存。

CVSS 6.2 · Medium EPSS 0.18% · P7

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking

Affected Version Matrix 1

VendorProduct Version RangeStatus
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
Vulnerability Title
Model Context Protocol MCP Ruby SDK 资源管理错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Model Context Protocol MCP Ruby SDK是Model Context Protocol组织的一个Ruby软件开发工具包组件。 Model Context Protocol MCP Ruby SDK 0.23.0之前版本存在资源管理错误漏洞，该漏洞源于使用IO#gets时未限制字节数，允许对等端发送无换行数据耗尽进程内存。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
modelcontextprotocol ruby-sdk < 0.23.0 -

II. Public POCs for CVE-2026-63119

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III. Intelligence Information for CVE-2026-63119

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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)

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
Same vendor: modelcontextprotocol
Same weakness: CWE-400

V. Comments for CVE-2026-63119

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