This challenge is part of the v8CTF, an exploit VRP for the v8 JavaScript engine.
See RULES.md for how to participate.
You can reach it at nc chrome-${MAJOR_VERSION}.v8ctf.ctfcompetition.com 1337, e.g. chrome-137.v8ctf.ctfcompetition.com.
It runs a chrome --headless=new on a user-provided URL. You can find the command line in chrome/challenge/chal and the Chrome version in chrome/challenge/Dockerfile.
The flag is at /flag/flag and is in the format v8CTF{.*}.
If you want to recreate the environment locally, check out https://google.github.io/kctf/ for tips on how to use the kCTF infrastructure.