Your question is Escalate and Contain Critical Bug. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
You're testing a high-impact release and uncover a bug that could materially affect users if it reaches production. You need to decide how severe it is, who to involve, and whether the right move is to block the release, ship with mitigations, or prepare a rollback.
Tell me about a time you found a critical bug. How did you assess the risk, communicate with stakeholders, decide on containment or rollback, and define what a successful resolution looked like?