Lab: CL.0 request smuggling

Summary: PortSwigger Research published a lab demonstrating CL.0 request smuggling, in which a back-end server ignores the Content-Length header on requests to some endpoints. The lab walks through probing endpoints by sending paired requests over a single connection, using requests for static files under /resources to cause a CL.0 desync, then smuggling a request to reach /admin and delete the user carlos.
What's compelling: A back-end that ignores Content-Length lets an attacker append a hidden request to a legitimate one, so a smuggled GET /admin/delete?username=carlos executes with the server's own trust in the connection - and the technique is drawn from real-world vulnerabilities, not a contrived scenario.

Read the original at PortSwigger Research ↗

Topics: Vulnerabilities & Patching
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