{"cve":"CVE-2026-52869","nvd":{"published":"2026-07-15T20:17:38.427","modified":"2026-10-24T21:10:00.130","status":"Analyzed","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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:L","score":7.1},"cwes":["CWE-639"],"references":["https://github.com/modelcontextprotocol/python-sdk/commit/1abcca2408a6b50e10ec601181f63f9978705c00","https://github.com/modelcontextprotocol/python-sdk/commit/ce267b6fc515dc4efc1dc70b6975b16ff0feef0a","https://github.com/modelcontextprotocol/python-sdk/pull/2690","https://github.com/modelcontextprotocol/python-sdk/pull/2719","https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.27.2"],"products":["lfprojects:mcp_python_sdk"],"source":"nvd","synced_at":"2026-10-25T17:50:08.599881581+00:00"},"epss":{"cve":"CVE-2026-52869","score":0.00535,"percentile":0.44844,"date":"2026-10-25"},"kev":null,"osv":[{"id":"GHSA-jpw9-pfvf-9f58","url":"https://osv.dev/vulnerability/GHSA-jpw9-pfvf-9f58","summary":"MCP Python SDK: HTTP transports serve session requests without verifying the authenticated principal","modified":"2026-09-10T03:50:52.526763662Z","packages":[{"ecosystem":"PyPI","name":"mcp","purl":"pkg:pypi/mcp","ranges":["<1.27.2"],"fixed":["1.27.2"]}]},{"id":"PYSEC-2026-3482","url":"https://osv.dev/vulnerability/PYSEC-2026-3482","summary":"MCP Python SDK: HTTP transports serve session requests without verifying the authenticated principal","modified":"2026-07-23T15:00:13.853115115Z","packages":[{"ecosystem":"PyPI","name":"mcp","purl":"pkg:pypi/mcp","ranges":["<1.27.2"],"fixed":["1.27.2"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}