> "What specifically are your concerns? What about what you've learned will create an exorbitant bill?"

Abusing the containers to send large amounts of outgoing traffic would do just that. Downloading files would do that too. How about sending a "while(true) { }" to hog some CPU? It doesn't take much to cause significant monetary damage.

Depending on their set-up, those containers could contain credentials or some other means to compromise the rest of the website. Perhaps it is possible to re-use the containers across different "sessions", serving multiple clients with malicious traffic. Those are plausible scenarios.

I'm not carrying out a full PT right now. Demonstrating the platform has been compromised is more than enough. Any other questions?