HTTP request smuggling
|Response status codes|
|Security access control methods|
HTTP request smuggling is a security exploit on the HTTP protocol that uses inconsistency between the interpretation of
Transfer-Encoding headers between HTTP server implementations in an HTTP proxy server chain. It was first documented in 2005 by Linhart et al.
This section relies largely or entirely on a single source. (November 2021)
In this type of HTTP request smuggling, the front end processes the request using Content-Length header while backend processes the request using Transfer-Encoding header.
In this type of HTTP request smuggling, the front end processes request using Transfer-Encoding header while backend processes the request using Content-Length header.
In this type of HTTP request smuggling, the front end and backend both process the request using Transfer-Encoding header, but the header can be obfuscated in a way (for example by nonstandard whitespace formatting or duplicate headers) that makes one of the servers but not the other one ignore it.
HTTP/2 is not vulnerable to request smuggling attacks as it uses a different method for determining the length of a request. Another method of avoiding the attack is for the frontend server to normalize HTTP requests before passing them to the backend, ensuring that they get interpreted in the same way. 
- "CWE - CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request Smuggling') (4.0)". cwe.mitre.org. Retrieved 2020-03-13.
- "What is HTTP request smuggling? Tutorial & Examples | Web Security Academy". portswigger.net. Retrieved 2020-03-13.
- Linhart, Chaim; Klein, Amit; Heled, Ronen; Orrin, Steve (2005). "HTTP request smuggling" (PDF).