Vulnerabilities in pkg:pypi/mcp

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-84m7-p3x7-pcfv",
  "modified" : "2026-10-15T20:13:13Z",
  "published" : "2026-10-15T20:13:13Z",
  "aliases" : [ "CVE-2026-59951" ],
  "summary" : "MCP Python SDK: Unbounded Session Accumulation in StreamableHTTP Transport Enables Resource Exhaustion",
  "details" : "### Summary\nIn affected versions, a Streamable HTTP server in stateful mode (the default) never reclaimed session state:\n\n- sessions did not expire;\n- a client `DELETE` ended the session but left its entry registered;\n- a session whose first request was refused stayed registered with a running task.\n\nEach session also kept its parsed `initialize` parameters, and the number of sessions was unlimited. A client that could reach the endpoint could grow server memory without bound using ordinary short requests; only a restart reclaimed it.\n\n### Am I affected?\nYes, if you serve MCP over Streamable HTTP in stateful mode and clients you do not fully trust can reach the endpoint. Stateful mode is the default for:\n\n- `FastMCP` (1.x)\n- `MCPServer` and `Server.streamable_http_app()` (2.x)\n- `StreamableHTTPSessionManager`\n\nAffected versions: 1.8.0 through 1.29.1, and 2.0.0 through 2.1.1.\n\nNot affected:\n\n- servers on 1.12.0 or later passing `stateless_http=True` (no sessions are kept)\n- servers using only the stdio or SSE transports\n\nAuthentication limits who can open sessions, not how many a token holder can open.\n\n### Fix\nUpgrade to `mcp` 1.30.0 (1.x) or 2.2.0 (2.x) or later. In those versions:\n\n- a session with no request in flight for `session_idle_timeout` seconds (default 1800) is closed and its ID then answers `404`; open streams and in-progress requests keep it alive;\n- at most `max_sessions` sessions exist at once (default 10000); a request that would open another is answered `503`;\n- a session is discarded as soon as it ends, whether by `DELETE`, expiry, or a refused opening request.\n\nBoth settings are keyword arguments on `FastMCP(...)` (1.x), `MCPServer.run()` / `streamable_http_app()` (2.x) and `StreamableHTTPSessionManager`; `None` disables them.\n\nThis bounds retention rather than eliminating it: a live session still holds its `initialize` parameters (up to roughly twice the 4 MiB body limit), and an `initialize` with invalid parameters still opens a session that expires like any other. On a small host, lower `session_idle_timeout`, `max_sessions` and `max_request_body_size` to fit.\n\nIf you cannot upgrade yet, pass `stateless_http=True` (1.12.0 or later) where you need no per-session state, or restrict who can reach the endpoint.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "mcp"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "1.8.0"
      }, {
        "fixed" : "1.30.0"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "mcp"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.0.0"
      }, {
        "fixed" : "2.2.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-84m7-p3x7-pcfv"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-59951"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/modelcontextprotocol/python-sdk/pull/3395"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/modelcontextprotocol/python-sdk/pull/3426"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/modelcontextprotocol/python-sdk/commit/92120b4b0f50385af096592d7cee932fc1d994e7"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/modelcontextprotocol/python-sdk/commit/d2290ca3434731b68ea3e2270bc06a6e6575931b"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/modelcontextprotocol/python-sdk"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.30.0"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/modelcontextprotocol/python-sdk/releases/tag/v2.2.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-400", "CWE-770", "CWE-772" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-10-15T20:13:13Z",
    "nvd_published_at" : "2026-10-14T17:18:29Z"
  }
}