Through novel research our team uncovered a critical vulnerability in Azure's guest user model, revealing that guest users can create and own subscriptions in external tenants they've joined—even without explicit privileges. This capability, which is often overlooked by Azure administrators, allows attackers to exploit these subscriptions to expand their access, move laterally within resource tenants, and create stealthy backdoor identities in the Entra directory. Alarmingly, Microsoft has confirmed real-world attacks using this method, highlighting a significant gap in many Azure threat models. This talk will share the findings from this first of its kind research into this exploit found in the wild.