{"id":"CVE-2026-52869","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-52869","generatedAt":"2026-10-28T02:56:36.719Z","title":"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…","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.","published":"2026-07-15T20:17:38.000Z","lastModified":"2026-10-24T21:10:00.000Z","status":"Analyzed","sourceIdentifier":"security-advisories@github.com","cvss":{"version":"3.1","score":7.1,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:L"},"cwe":["CWE-639"],"affected":["lfprojects/mcp python sdk"],"epss":{"score":0.00535,"percentile":0.44864,"date":"2026-10-26","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"high","text":"High impact if exploited, but EPSS currently rates exploitation as unlikely (0.53%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit."},"changes":[],"references":[{"url":"https://github.com/modelcontextprotocol/python-sdk/commit/1abcca2408a6b50e10ec601181f63f9978705c00","tags":["Patch"],"source":"security-advisories@github.com"},{"url":"https://github.com/modelcontextprotocol/python-sdk/commit/ce267b6fc515dc4efc1dc70b6975b16ff0feef0a","tags":["Patch"],"source":"security-advisories@github.com"},{"url":"https://github.com/modelcontextprotocol/python-sdk/pull/2690","tags":["Issue Tracking","Patch"],"source":"security-advisories@github.com"},{"url":"https://github.com/modelcontextprotocol/python-sdk/pull/2719","tags":["Issue Tracking","Patch"],"source":"security-advisories@github.com"},{"url":"https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.27.2","tags":["Release Notes"],"source":"security-advisories@github.com"},{"url":"https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-jpw9-pfvf-9f58","tags":["Vendor Advisory"],"source":"security-advisories@github.com"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-52869","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}