{
 "id": "CVE-2026-52869",
 "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": "2026-07-15",
 "last_modified": "2026-10-24",
 "vuln_status": "Analyzed",
 "cna": "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",
  "source": "security-advisories@github.com"
 },
 "cwe": [
  "CWE-639"
 ],
 "products": [
  {
   "vendor": "lfprojects",
   "product": "mcp_python_sdk",
   "versions_affected": "< 1.27.2",
   "fixed_in": "1.27.2",
   "product_id": null
  }
 ],
 "category": "protocol",
 "surface": [
  "auth_bypass"
 ],
 "kev": null,
 "fix": {
  "status": "fixed",
  "version": "1.27.2",
  "url": "https://github.com/modelcontextprotocol/python-sdk/commit/1abcca2408a6b50e10ec601181f63f9978705c00"
 },
 "references": [
  {
   "url": "https://github.com/modelcontextprotocol/python-sdk/commit/1abcca2408a6b50e10ec601181f63f9978705c00",
   "source": "security-advisories@github.com",
   "tags": [
    "Patch"
   ]
  },
  {
   "url": "https://github.com/modelcontextprotocol/python-sdk/commit/ce267b6fc515dc4efc1dc70b6975b16ff0feef0a",
   "source": "security-advisories@github.com",
   "tags": [
    "Patch"
   ]
  },
  {
   "url": "https://github.com/modelcontextprotocol/python-sdk/pull/2690",
   "source": "security-advisories@github.com",
   "tags": [
    "Issue Tracking",
    "Patch"
   ]
  },
  {
   "url": "https://github.com/modelcontextprotocol/python-sdk/pull/2719",
   "source": "security-advisories@github.com",
   "tags": [
    "Issue Tracking",
    "Patch"
   ]
  },
  {
   "url": "https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.27.2",
   "source": "security-advisories@github.com",
   "tags": [
    "Release Notes"
   ]
  },
  {
   "url": "https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-jpw9-pfvf-9f58",
   "source": "security-advisories@github.com",
   "tags": [
    "Vendor Advisory"
   ]
  }
 ],
 "related_agents": [
  "modelcontextprotocol-python-sdk",
  "modelcontextprotocol-typescript-sdk"
 ],
 "related_incidents": [],
 "match": {
  "tests": [
   "A:name",
   "B:vocabulary"
  ],
  "terms": [
   "mcp-sdk:MCP Python SDK",
   "model context protocol"
  ]
 },
 "status": "candidate",
 "note": null,
 "reviewer": null,
 "checked_on": null,
 "retrieved_on": "2026-10-26"
}