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CVE-2026-52869— MCP Python SDK: HTTP transports serve session requests without verifying the authenticated principal

CVSS 7.1 · High EPSS 0.25% · P16

Possible ATT&CK Techniques 1AI

T1133 · External Remote Services

Affected Version Matrix 1

VendorProductVersion RangeStatus
modelcontextprotocolpython-sdk< 1.27.2affected
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I. Basic Information for CVE-2026-52869

Vulnerability Information
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Vulnerability Title
MCP Python SDK: HTTP transports serve session requests without verifying the authenticated principal
Source: NVD (National Vulnerability Database)
Vulnerability Description
The MCP Python SDK, called mcp on PyPI, is a Python implementation of the Model Context Protocol (MCP). Prior to 1.27.2, the SSE and stateful Streamable HTTP transports mcp.server.sse.SseServerTransport and mcp.server.streamable_http_manager.StreamableHTTPSessionManager route requests to existing sessions using only the session_id query parameter or Mcp-Session-Id header without verifying the authenticated principal that created the session, allowing a different bearer-token-authenticated client with a known session ID to inject JSON-RPC messages into that session. This issue is fixed in version 1.27.2.
Source: NVD (National Vulnerability Database)
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:L
Source: NVD (National Vulnerability Database)
Vulnerability Type
通过用户控制密钥绕过授权机制
Source: NVD (National Vulnerability Database)
Vulnerability Title
Model Context Protocol MCP Python SDK 授权问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Model Context Protocol MCP Python SDK是Model Context Protocol组织的一款Python软件开发工具包。 Model Context Protocol MCP Python SDK 1.27.2之前版本存在授权问题漏洞，该漏洞源于SSE和有状态的Streamable HTTP传输仅使用session_id查询参数或Mcp-Session-Id标头将请求路由到现有会话，而未验证创建该会话的认证主体，允许知道会话ID的、通过bearer-token认证的不
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

VendorProductAffected VersionsCPESubscribe
modelcontextprotocolpython-sdk < 1.27.2 -

II. Public POCs for CVE-2026-52869

#POC DescriptionSource LinkShenlong Link
AI-Generated POCPremium
Qwen3.6-35B-A3B · 9542 chars
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III. Intelligence Information for CVE-2026-52869

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Patches & Fixes for CVE-2026-52869 (3)

Vendor Advisories for CVE-2026-52869 (1)

Vendor Pages for CVE-2026-52869 (1)

Same Patch Batch · modelcontextprotocol · 2026-07-15 · 3 CVEs total

CVE-2026-528707.6 HIGHMCP Python SDK: Experimental task handlers allow any client to access and cancel other cli
CVE-2026-59950MCP Python SDK: WebSocket server transport does not support Host/Origin validation

IV. Related Vulnerabilities

Same product: python-sdk
Same vendor: modelcontextprotocol
Same weakness: CWE-639

V. Comments for CVE-2026-52869

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