CVE-2019-16785: Inconsistent Interpretation of HTTP Requests (HTTP Request Smuggling)
(updated )
Waitress implemented an optional part of the RFC7230 which states: “Although the line terminator for the start-line and header fields is the sequence CRLF, a recipient may recognize a single LF as a line terminator and ignore any preceding CR.” Unfortunately if a front-end server does not parse header fields with an LF the same way as it does those with a CRLF it can lead to the front-end and the back-end server parsing the same HTTP message in two different ways. This can lead to a potential for HTTP request smuggling/splitting whereby Waitress may see two requests while the front-end server only sees a single HTTP message.
References
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