Rooted! Learned a very valuable lesson with this one: Don’t overlook the obvious!
Hints:
Foothold: Thorough scan. Don’t skip anything. Investigate everything! Something will stand out. Research and you’ll find plenty of resources to and even something juicy to use. Make your adjustments based on what you’ve found so far and you’re in.
User: Enumerate. A popular script can help. You’ll know what to do once you find the loot. You won’t have to look far. Now think what you could do with it. Use it where you think it should work.
Root: You should have come across this in your initial investigation, except you were missing something then, which you now have. Try it!
Thanks to @TheCyberGeek. Enjoyed this one.