{"id":"CVE-2026-52869","state":"PUBLISHED","title":"MCP Python SDK: HTTP transports serve session requests without verifying the authenticated principal","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.","publishedAt":"2026-07-15T20:06:23.604Z","updatedAt":"2026-07-16T13:00:37.854Z","severity":{"score":7.1,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:L","source":"GitHub_M"},"assigner":"GitHub_M","products":["modelcontextprotocol python-sdk"],"affected":[{"vendor":"modelcontextprotocol","product":"python-sdk","versions":[{"version":"< 1.27.2","status":"affected"}]}],"references":["https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-jpw9-pfvf-9f58","https://github.com/modelcontextprotocol/python-sdk/pull/2690","https://github.com/modelcontextprotocol/python-sdk/pull/2719","https://github.com/modelcontextprotocol/python-sdk/commit/1abcca2408a6b50e10ec601181f63f9978705c00","https://github.com/modelcontextprotocol/python-sdk/commit/ce267b6fc515dc4efc1dc70b6975b16ff0feef0a","https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.27.2"],"weaknesses":["CWE-639"],"ingestedAt":"2026-10-29T20:12:16.098Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/52xxx/CVE-2026-52869.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-52869","state":"PUBLISHED","datePublished":"2026-07-15T20:06:23.604Z","dateUpdated":"2026-07-16T13:00:37.854Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-06-08T21:44:27.363Z"},"containers":{"cna":{"title":"MCP Python SDK: HTTP transports serve session requests without verifying the authenticated principal","descriptions":[{"lang":"en","value":"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."}],"affected":[{"vendor":"modelcontextprotocol","product":"python-sdk","versions":[{"version":"< 1.27.2","status":"affected"}]}],"references":[{"url":"https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-jpw9-pfvf-9f58","name":"https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-jpw9-pfvf-9f58","tags":["x_refsource_CONFIRM"]},{"url":"https://github.com/modelcontextprotocol/python-sdk/pull/2690","name":"https://github.com/modelcontextprotocol/python-sdk/pull/2690","tags":["x_refsource_MISC"]},{"url":"https://github.com/modelcontextprotocol/python-sdk/pull/2719","name":"https://github.com/modelcontextprotocol/python-sdk/pull/2719","tags":["x_refsource_MISC"]},{"url":"https://github.com/modelcontextprotocol/python-sdk/commit/1abcca2408a6b50e10ec601181f63f9978705c00","name":"https://github.com/modelcontextprotocol/python-sdk/commit/1abcca2408a6b50e10ec601181f63f9978705c00","tags":["x_refsource_MISC"]},{"url":"https://github.com/modelcontextprotocol/python-sdk/commit/ce267b6fc515dc4efc1dc70b6975b16ff0feef0a","name":"https://github.com/modelcontextprotocol/python-sdk/commit/ce267b6fc515dc4efc1dc70b6975b16ff0feef0a","tags":["x_refsource_MISC"]},{"url":"https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.27.2","name":"https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.27.2","tags":["x_refsource_MISC"]}],"metrics":[{"cvssV3_1":{"attackComplexity":"HIGH","attackVector":"NETWORK","availabilityImpact":"LOW","baseScore":7.1,"baseSeverity":"HIGH","confidentialityImpact":"HIGH","integrityImpact":"HIGH","privilegesRequired":"LOW","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:L","version":"3.1"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-639","lang":"en","description":"CWE-639: Authorization Bypass Through User-Controlled Key","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-07-15T20:06:23.604Z"},"source":{"advisory":"GHSA-jpw9-pfvf-9f58","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-07-16T13:00:22.816039Z","id":"CVE-2026-52869","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"total"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-07-16T13:00:37.854Z"}}]}}}