Analysis Summary

A newly discovered critical vulnerability in Apple’s iOS activation infrastructure, specifically affecting the latest iOS 18.5 stable release as of May 2025, exposes millions of devices to pre-activation tampering. This flaw allows attackers to inject unauthenticated XML payloads during the initial setup phase without any requirement for authentication or digital signature verification. The vulnerability centers around Apple’s internal endpoint, https://humb.apple.com/humbug/baa, which handles device provisioning requests during activation. By exploiting this endpoint, malicious actors can manipulate configuration data silently and persistently, impacting both individual users and enterprise-level device enrollments.

Security analysts revealed that the vulnerability stems from the backend server’s inadequate validation mechanisms for incoming XML payloads. Through extensive testing, it was discovered that the server tolerates malformed XML content and supports insecure features like DOCTYPE declarations, opening the door for various attack vectors. Attackers can exploit this behavior by submitting specially crafted .plist (XML Property List) files during the device setup process, which the server incorrectly processes without raising errors. This lack of error feedback leaves both the device and Apple’s monitoring systems unaware of any tampering.

The technical root of this issue lies in the server’s insecure XML parsing implementation, which fails to apply standard security practices when handling external input. During activation, devices submit XML-formatted provisioning data containing identifiers and setup instructions. However, due to the absence of signature verification, the server cannot authenticate the origin of these payloads, allowing attackers to impersonate Apple and submit malicious configuration data. These payloads can even include XML External Entity (XXE) constructs, enabling attackers to read internal files or initiate other forms of XML-based attacks, all while remaining undetected.

This vulnerability raises serious concerns regarding the integrity and security of Apple’s activation ecosystem, especially for enterprises that rely on strict device provisioning policies for compliance. The ability to silently manipulate provisioning data during the earliest phase of device operation creates a persistent threat that could survive through future updates. The lack of validation and monitoring underscores a broader lapse in backend security hygiene at Apple, signaling a need for immediate architectural review and patching to safeguard millions of iOS devices from covert configuration manipulation and unauthorized access.

Impact

• Gain Access
• Security Bypass

Affected Vendors

Remediation

• Apple must implement mandatory digital signature checks on all XML provisioning payloads to ensure authenticity and prevent tampering.
• Harden the XML parser on the activation server by disabling support for DOCTYPE to mitigate risks like XML External Entity (XXE) attacks.
• Apply strict schema validation for .plist files and reject any malformed or non-conforming XML payloads at the activation endpoint.
• Deploy anomaly detection systems to monitor provisioning traffic and flag unusual or malformed requests to the endpoint.
• Require authenticated and signed requests from verified Apple-controlled sources or trusted MDM systems before processing any provisioning data.
• Conduct a comprehensive code and infrastructure review of the https://humb.apple.com/humbug/baa endpoint to close any input validation or parsing gaps.
• Restrict access to sensitive provisioning endpoints from external networks, especially during pre-activation phases.
• For high-risk deployments, require devices to re-initiate activation using patched backend infrastructure once Apple resolves the issue.
• Apple should issue a security advisory and notify organizations using Apple Business/School Manager or MDM platforms about the risk.
• Release an urgent iOS patch (18.5.1 or later) that includes client-side changes to reject insecure or unsigned provisioning responses.