CVE-2026-67430— MCP Ruby SDK: Unbounded session retention in StreamableHTTPTransport allows memory exhaustion via initialize flood
Possible ATT&CK Techniques 2AI
T1068 · Exploitation for Privilege Escalation T1499 · Endpoint Denial of ServiceAffected Version Matrix 1
| Vendor | Product | Version Range | Status |
|---|---|---|---|
| modelcontextprotocol | ruby-sdk | < 0.23.0 | affected |
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I. Basic Information for CVE-2026-67430
Vulnerability Information
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Vulnerability Title
MCP Ruby SDK: Unbounded session retention in StreamableHTTPTransport allows memory exhaustion via initialize flood
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 expire sessions by default, so repeated initialize requests retain unbounded ServerSession objects and can exhaust process memory. This issue is fixed in version 0.23.0.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
在移除最后引用时对内存的释放不恰当(内存泄露)
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StreamableHTTPTransport默认不过期会话，重复初始化请求导致无界ServerSession对象，可能耗尽进程内存。
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-2026-67430
| # | POC Description | Source Link | Shenlong Link |
|---|
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Patches & Fixes for CVE-2026-67430 (1)
Vendor Advisories for CVE-2026-67430 (1)
Vendor Pages for CVE-2026-67430 (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-2026-63119 | 6.2 MEDIUM | MCP Ruby SDK: Unbounded line buffer in stdio transports leads to memory exhaustion (DoS) |
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-2026-63119
MCP Ruby SDK: Unbounded line buffer in stdio transports lead - 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-2026-63119
MCP Ruby SDK: Unbounded line buffer in stdio transports lead - CVE-2026-63118
MCP Ruby SDK: Streamable HTTP transport lacks DNS-rebinding - CVE-2026-59950
MCP Python SDK: WebSocket server transport does not support
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