CVE-2017-7139 in iOS
Summary
by MITRE
An issue was discovered in certain Apple products. iOS before 11 is affected. The issue involves the "Phone" component. It allows attackers to obtain sensitive information by leveraging a timing bug to read a secure-content screenshot that occurred during a locking action.
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Analysis
by VulDB Data Team • 01/19/2021
The vulnerability identified as CVE-2017-7139 represents a significant security flaw within Apple's iOS operating system affecting versions prior to iOS 11. This issue specifically targets the Phone component and demonstrates a critical timing-based information disclosure vulnerability that could potentially compromise user privacy and sensitive data. The flaw exploits a race condition that occurs during the screenshot capture process when the device is locked, creating a window of opportunity for attackers to access secure content that should otherwise remain protected.
The technical implementation of this vulnerability stems from a timing bug within the iOS screenshot mechanism that occurs during device lock operations. When a user locks their iOS device, the system captures a screenshot of the current screen as part of its security protocols. However, due to improper synchronization between the locking process and the screenshot capture functionality, attackers can manipulate timing conditions to intercept and read secure content from these screenshots. This vulnerability operates at the kernel level and leverages the inherent race condition between the device lock sequence and the secure screenshot generation process, making it particularly challenging to detect and prevent through standard security measures.
The operational impact of CVE-2017-7139 extends beyond simple information disclosure, as it represents a fundamental flaw in iOS security architecture that could enable attackers to access sensitive information including contact details, call logs, and potentially other private data displayed on the lock screen. This vulnerability aligns with CWE-367, which describes a Time-of-Check to Time-of-Use (TOCTOU) race condition, where the system state changes between the time of checking and the time of using the resource. The attack vector specifically targets the lock screen functionality and could be exploited through automated timing attacks, making it particularly dangerous as it requires minimal user interaction to potentially compromise sensitive information.
Security researchers have classified this vulnerability as a critical risk due to its ability to bypass iOS security controls through timing manipulation. The flaw demonstrates how seemingly benign system operations can create security vulnerabilities when proper synchronization mechanisms are absent. Organizations and users should consider this vulnerability in the context of broader ATT&CK framework categories related to privilege escalation and credential access, as it could potentially serve as a stepping stone for more sophisticated attacks. The vulnerability also highlights the importance of proper input validation and synchronization in mobile operating systems, particularly when dealing with secure content and system lock mechanisms.
Mitigation strategies for CVE-2017-7139 primarily focus on updating to iOS 11 or later versions where Apple has implemented proper synchronization mechanisms to prevent the timing race condition. System administrators should ensure all iOS devices within their environment are updated to the latest available versions to eliminate exposure to this vulnerability. Additionally, organizations should implement comprehensive mobile device management policies that enforce automatic updates and monitor for unpatched devices. The vulnerability serves as a reminder of the critical importance of proper race condition handling in security-sensitive applications and the necessity of thorough testing of system interactions during security-critical operations.