CVE-2019-8699 in iOS
Summary
by MITRE
A logic issue existed in the handling of answering phone calls. The issue was addressed with improved state management. This issue is fixed in iOS 12.4. The initiator of a phone call may be able to cause the recipient to answer a simultaneous Walkie-Talkie connection.
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Analysis
by VulDB Data Team • 07/11/2020
The vulnerability described in CVE-2019-8699 represents a significant security flaw in iOS telecommunications handling mechanisms that could potentially enable unauthorized call control operations. This logic flaw existed within the phone call answering process specifically affecting how the system managed concurrent call states and Walkie-Talkie functionality. The issue was classified as a state management problem that allowed for improper handling of simultaneous connection scenarios, creating an exploitable condition where one party could manipulate another's call answering behavior. The vulnerability was addressed through enhanced state management protocols within the iOS operating system, specifically targeting the core telecommunications framework that governs how phone calls are processed and managed.
The technical implementation of this vulnerability stems from inadequate state validation during call initiation and answering processes. When a user initiates a phone call, the system maintains various internal states to track connection progress and handle user interactions. The flaw occurred when the system failed to properly validate the sequence of events during simultaneous connection handling, particularly when Walkie-Talkie functionality was involved. This condition created a scenario where the call initiator could manipulate the system's understanding of call states, potentially causing the recipient's device to automatically answer an incoming call or Walkie-Talkie connection. The vulnerability is categorized under CWE-284 which addresses improper access control and improper privilege management in system operations, specifically within telecommunications contexts where state transitions must be carefully controlled.
From an operational perspective, this vulnerability posed a serious risk to user privacy and call integrity within the iOS ecosystem. The ability for one party to force another to answer a call represents a significant breach of user control over their communication devices and could enable various malicious activities including unwanted call interception, privacy violations, and potential social engineering attacks. Attackers could exploit this condition to gain unauthorized access to communication channels, particularly in scenarios involving Walkie-Talkie functionality where real-time communication is expected. The vulnerability was particularly concerning because it operated at a fundamental level of the operating system's telecommunications handling, making it difficult to detect and potentially allowing for persistent exploitation if not properly addressed through system updates.
The remediation for CVE-2019-8699 involved implementing enhanced state management protocols that properly validate call sequence transitions and ensure proper handling of concurrent connection scenarios. Apple's fix focused on strengthening the internal state validation mechanisms within the telephony framework to prevent unauthorized state manipulation during call initiation and answering processes. This update specifically targeted the Walkie-Talkie functionality integration and ensured that proper user consent and system state validation occurred before any automatic answering operations could be triggered. The solution aligns with ATT&CK framework techniques related to privilege escalation and operating system manipulation, where attackers might attempt to exploit system-level communication handling to gain unauthorized control over device operations.
The vulnerability demonstrates the critical importance of proper state management in telecommunications systems and highlights how seemingly minor logic flaws can create significant security implications. The fix represents a comprehensive approach to addressing state validation issues that could affect the integrity of user communication and system behavior. This type of vulnerability underscores the need for rigorous testing of concurrent operation scenarios and proper validation of system state transitions, particularly in environments where user privacy and communication control are paramount. The remediation approach taken by Apple provides a model for addressing similar state management issues in other telecommunications and operating system contexts, emphasizing the importance of maintaining strict control over system operations and user interaction sequences.