{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "cpe": "cpe:2.3:a:lfprojects:mcp_python_sdk:*:*:*:*:*:*:*:*",
            "extracted_events": [
              {
                "introduced": "0"
              },
              {
                "fixed": "1.27.2"
              }
            ],
            "source": [
              "CPE_RANGE",
              "REFERENCES"
            ]
          },
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "62137874ff26dd74d2fea80ff528a7fd9ca7a5e7"
            },
            {
              "fixed": "1abcca2408a6b50e10ec601181f63f9978705c00"
            },
            {
              "fixed": "ce267b6fc515dc4efc1dc70b6975b16ff0feef0a"
            }
          ],
          "repo": "https://github.com/modelcontextprotocol/python-sdk",
          "type": "GIT"
        }
      ]
    }
  ],
  "aliases": [
    "GHSA-jpw9-pfvf-9f58"
  ],
  "database_specific": {
    "cna_assigner": "GitHub_M",
    "cwe_ids": [
      "CWE-639"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/52xxx/CVE-2026-52869.json"
  },
  "details": "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.",
  "id": "CVE-2026-52869",
  "modified": "2026-07-19T03:30:56.683852109Z",
  "published": "2026-07-15T20:06:23.604Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.27.2"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/52xxx/CVE-2026-52869.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-jpw9-pfvf-9f58"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-52869"
    },
    {
      "type": "FIX",
      "url": "https://github.com/modelcontextprotocol/python-sdk/commit/1abcca2408a6b50e10ec601181f63f9978705c00"
    },
    {
      "type": "FIX",
      "url": "https://github.com/modelcontextprotocol/python-sdk/commit/ce267b6fc515dc4efc1dc70b6975b16ff0feef0a"
    },
    {
      "type": "FIX",
      "url": "https://github.com/modelcontextprotocol/python-sdk/pull/2690"
    },
    {
      "type": "FIX",
      "url": "https://github.com/modelcontextprotocol/python-sdk/pull/2719"
    }
  ],
  "schema_version": "1.8.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "MCP Python SDK: HTTP transports serve session requests without verifying the authenticated principal"
}