Lab: HTTP request smuggling, confirming a TE.CL vulnerability via differential responses
Summary: This PortSwigger lab sets up a front-end and back-end server where the back-end does not support chunked encoding, and the task is to smuggle a request so that a later request for the web root returns a 404 Not Found. The lab supports HTTP/2, but the intended solution uses techniques only possible in HTTP/1, with the request issued twice through Burp Repeater after unchecking the "Update Content-Length" option.
Bottom line: The exercise turns on a mismatch between what the front-end and back-end servers each believe about request boundaries, the same parsing gap that lets an attacker slip a hidden request past the front door and have the back-end act on it.
Read the original at PortSwigger Research ↗
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