Tornado vulnerable to HTTP request smuggling via improper parsing of `Content-Length` fields and chunk lengths
Summary
Tornado interprets -, +, and _ in chunk length and Content-Length values, which are not allowed by the HTTP RFCs. This can result in request smuggling when Tornado is deployed behind certain proxies that interpret those non-standard characters differently. This is known to apply to older versions of haproxy, although the current release is not affected.
Details
Tornado uses the int constructor to parse the values of Content-Length headers and chunk lengths in the following locations:
tornado/http1connection.py:445
self._expected_content_remaining = int(headers["Content-Length"])
tornado/http1connection.py:621
content_length = int(headers["Content-Length"]) # type: Optional[int]
tornado/http1connection.py:671
chunk_len = int(chunk_len_str.strip(), 16)
Because int("0_0") == int("+0") == int("-0") == int("0"), using the int constructor to parse and validate strings that should contain only ASCII digits is not a good strategy.
Deep Security Visibility Without the Complexity
SynScan provides clear, real-time security insights so you can monitor your attack surface, spot risks early, and act fast—without extra complexity.
- No setup fees
- 5-min deployment
- Cancel anytime