Lab: HTTP request smuggling, obfuscating the TE header

Summary: This PortSwigger lab presents a front-end and back-end server that handle duplicate HTTP request headers differently, with the front-end rejecting any method other than GET or POST. The goal is to smuggle a request so the back-end processes the next request as using the method GPOST, which requires HTTP/1-only techniques and a trailing \r\n\r\n after the final 0.
Why it matters: The lab's success condition is a back-end server accepting a method the front-end was built to reject, which is the same gap an attacker uses to slip a request past the perimeter control your architecture trusts.

Read the original at PortSwigger Research ↗

Topics: Vulnerabilities & Patching
Related: Attackers Exploit UnrealIRCd Flaw That Enables Server-Level Command Injection Cyber Risks · Nov 14, 2026
U.S. CISA adds Check Point and UnrealIRCd flaws to its Known Exploited Vulnerabilities catalog Cyber Risks · Nov 14, 2026
PostgreSQL Patches 52 Flaws, Including 22-Year-Old Bug Enabling Authenticated RCE Cyber Risks · Nov 13, 2026