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CVE-2026-67431— MCP Ruby SDK: Ruby SSE Session Poisoning

Quick assessment

Affected
modelcontextprotocol ruby-sdk
Exploitation
Public or AI PoC available; prioritize validation
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之前版本存在权限许可和访问控制问题漏洞，该漏洞源于StreamableHTTPTransport未将会话ID绑定到会话所有者，允许攻击者使用窃取的会话ID发送tools/call请求在受害者会话中执行。

CVSS 8.3 · High EPSS 0.48% · P39

Possible ATT&CK Techniques 1 AI

T1133 · External Remote Services

Affected Version Matrix 1

VendorProduct Version RangeStatus
modelcontextprotocol ruby-sdk < 0.23.0 affected
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I. Basic Information for CVE-2026-67431

Vulnerability Information
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Vulnerability Title
MCP Ruby SDK: Ruby SSE Session Poisoning
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::StreamableHTTPTransport in the mcp gem does not bind a session ID to a session owner, allowing an attacker with a stolen session ID to send tools/call requests that execute in the victim's session. This issue is fixed in version 0.23.0.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
访问控制不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
Model Context Protocol MCP Ruby SDK 权限许可和访问控制问题漏洞
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之前版本存在权限许可和访问控制问题漏洞，该漏洞源于StreamableHTTPTransport未将会话ID绑定到会话所有者，允许攻击者使用窃取的会话ID发送tools/call请求在受害者会话中执行。
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-2026-67431

# POC Description Source Link Shenlong Link
AI-Generated POC Premium
Qwen3.6-35B-A3B · 6738 chars
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Trigger conditions & impact
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POC zip download
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III. Intelligence Information for CVE-2026-67431

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Patches & Fixes for CVE-2026-67431 (1)

Vendor Advisories for CVE-2026-67431 (1)

Vendor Pages for CVE-2026-67431 (1)

Same Patch Batch · modelcontextprotocol · 2026-07-29 · 5 CVEs total

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-2026-63119 6.2 MEDIUM MCP Ruby SDK: Unbounded line buffer in stdio transports leads to memory exhaustion (DoS)
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-284

V. Comments for CVE-2026-67431

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