A critical security vulnerability has been discovered in Apple’s iOS activation infrastructure that allows attackers to inject unauthenticated XML payloads during the device setup phase.

This flaw, affecting the latest iOS 18.5 stable release as of May 2025, exposes millions of Apple devices to potential pre-activation tampering and persistent configuration manipulation without requiring any form of authentication or signature verification.

The vulnerability targets Apple’s internal activation endpoint at https://humb.apple.com/humbug/baa, which processes device provisioning requests during the initial setup process.

Attackers can exploit this weakness by sending malformed XML.plist payloads that the server accepts and processes without proper validation, creating opportunities for unauthorized configuration changes that persist beyond the activation phase.

Substack analysts identified this vulnerability through extensive testing of the iOS activation backend, revealing that the server’s tolerance for malformed content and support for DOCTYPE declarations creates multiple attack vectors.

The research demonstrates how the activation infrastructure’s lack of sender verification mechanisms allows arbitrary provisioning modifications to occur silently, with no error feedback provided to either the device or Apple’s monitoring systems.

Technical Attack Mechanism

The core vulnerability lies in the activation server’s XML parsing implementation, which fails to implement basic security controls typically required for processing external data.

When a device initiates the activation process, it communicates with Apple’s backend through XML-formatted requests containing device identifiers and provisioning information.

The server’s acceptance of unsigned payloads means attackers can craft malicious XML documents that modify device configurations during activation.

These payloads can include DOCTYPE declarations that potentially enable XML External Entity (XXE) attacks or other XML-based exploitation techniques.

The lack of signature verification means the server cannot distinguish between legitimate Apple-generated provisioning data and attacker-controlled content, making this vulnerability particularly dangerous for enterprise deployments where device provisioning policies are critical for security compliance.

This discovery highlights significant gaps in Apple’s backend security validation processes, potentially affecting the integrity of device configurations across the entire iOS ecosystem.

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