Description

A critical vulnerability has been uncovered in Apple’s iOS activation backend, specifically at the endpoint https://humb.apple.com/humbug/baa, allowing attackers to inject unsigned XML .plist payloads during device setup. Verified on iOS 18.5 (as of May 2025), the flaw bypasses signature checks and sender authentication, enabling unauthorized provisioning and configuration changes before activation is complete. The endpoint accepts malformed XML, including DOCTYPE declarations, making it vulnerable to XML External Entity (XXE) attacks and multi-stage payload injections. This flaw can be exploited remotely through captive portals, rogue Wi-Fi networks, or even compromised supply chain environments. Devices are at risk before the user can enroll them in Mobile Device Management (MDM) or apply security policies. The server responds with an HTTP 200 OK to these malicious payloads, confirming server-side processing of Base64-encoded instructions that can override MDM controls, silently install persistent profiles, and alter critical system behavior. Forensics on affected iOS 18.5 devices revealed unauthorized entries in CloudKitAccountInfoCache and CommCenter, with unexplained configuration changes appearing after activation. The vulnerability poses a significant threat to device integrity, especially in high-security environments. Its ability to plant logic before activation could explain anomalies in events like SignalGate, where encrypted communications were compromised without forensic traces. Despite being disclosed to Apple on May 19, 2025, the vulnerability remains unpatched. IT teams, enterprise admins, and end-users are strongly advised to avoid untrusted networks during device setup and to monitor for signs of unexpected behavior. This issue highlights the critical need for robust validation in Apple's activation infrastructure and reveals a dangerous blind spot in iOS device security during its most vulnerable stage.