Lab: the helpful ping box
A diagnostic page shells out. Get it to introduce itself.
Read the ping wrapper and find the concatenation. Ping a normal host first for the baseline, then append a second command with a separator: the page runs as a web user, and asking who it is tells you exactly what an attacker inherits.
That was the whole lesson.
A free account adds the interactive part: the marking quiz, the lab if this lesson carries one, live progress, the timed exam, and a certificate employers can verify.