Your question is Leading Through a Zero-Day Incident. 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).
Tell me about a time you discovered or were first to recognize a severe security vulnerability in a critical production system. Walk me through how you assessed the risk, prioritized immediate containment versus business continuity, coordinated stakeholders, and what the outcome was.