Google Cloud’s Identity-Aware Proxy (IAP) is often seen as the final gatekeeper for internal GCP services - but what happens when that gate quietly swings open? This session uncovers how subtle misconfigurations in IAP can lead to serious data exposure, even in environments with no public IPs, strict VPC Service Controls, and hardened perimeters. We’ll introduce a new vulnerability in IAP that enables data exfiltration, allowing attackers to bypass traditional network controls entirely, without ever sending traffic to the public internet. In addition, we’ll walk through real-world examples of overly permissive IAM bindings, misplaced trust in user-supplied headers, and overlooked endpoints that quietly expand the attack surface. Attendees will gain a deeper understanding of IAP’s internal workings, practical detection strategies, and a critical perspective on trust boundaries in GCP.