Apple iOS Activation Vulnerability Permits Unauthenticated XML Payload Injection

A critical vulnerability has surfaced in Apple’s iOS activation infrastructure, threatening the integrity of device provisioning during the setup phase.

Security researchers have identified that the backend endpoint responsible for device activation on iOS 18.5 the latest stable release as of May 2025 accepts unauthenticated and unsigned XML property list (.plist) payloads, exposing Apple devices to serious pre-activation tampering risks.

Arbitrary Provisioning Without Authentication

The vulnerability centers on the Apple internal endpoint https://humb.apple.com/humbug/baa, which processes provisioning logic during device setup.

It was discovered that this activation server not only fails to require sender authentication but also processes XML payloads without signature verification or even proper error handling.

The server tolerates malformed inputs and accepts XML files with DOCTYPE declarations, a known vector for XML External Entity (XXE) attacks.

According to the Report, this gap in backend validation allows arbitrary provisioning changes to be injected into the device activation workflow.

Attackers exploiting this flaw can introduce persistent configuration manipulations and custom provisioning logic, completely bypassing standard Mobile Device Management (MDM) enrollment, user consent, and Apple’s signature checks.

Server-Side Processing of Malicious Payloads

Researchers demonstrated the exploit using a crafted XML plist payload containing custom keys such as CloudKitAccountInfoCache with embedded SHA256-hashed and base64-encoded data.

The server consistently responded with an HTTP 200 OK, confirming server-side acceptance and processing of the illicit payloads.

Notably, exploitation does not require a jailbreak, physical access, or advanced persistence techniques; it can be delivered remotely via captive portal networks, rogue access points, or compromised provisioning servers making it particularly dangerous during mass deployments or in high-risk environments.

The real-world implications of this vulnerability are far-reaching. Successful attackers gain the ability to inject persistent profiles, alter network and modem configuration policies (such as AllowedProtocolMask), and even introduce silent background tasks.

These modifications are executed either immediately during setup or post-activation, all without user interaction or visibility from standard security logs.

Forensic analysis on devices freshly reset and activated on iOS 18.5 revealed persistent entries in system caches such as CloudKitAccountInfoCache and CommCenter, as well as configuration drifts that could not be attributed to any user action.

Server logs and sysdiagnose data further confirmed the acceptance of unsigned and unverified provisioning payloads.

Security experts point to similarities between this vulnerability and the techniques employed in large-scale incidents such as the so-called SignalGate event where secure communications and critical app functions were subverted without leaving conventional device forensics.

The ability to plant logic before a device ever reaches the user’s hands dramatically increases the stealth and persistence of potential attacks, particularly in supply chain or enterprise contexts.

Disclosure attempts to Apple were made on May 19, but no vendor response has been reported as of publication.

The lack of remediation leaves iOS devices, including those running the latest stable release, vulnerable to advanced post-exploitation tactics, warranting immediate attention from both Apple and enterprise security teams.

As this vulnerability remains unmitigated, it underscores the urgent need for improved authentication, payload verification, and robust error handling in critical infrastructure components underpinning device trust, especially at the earliest stages of setup and activation.

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