CVE-2018-4428 in iOS
Summary
by MITRE • 10/28/2020
A lock screen issue allowed access to the share function on a locked device. This issue was addressed by restricting options offered on a locked device. This issue is fixed in iOS 12.1.1. A local attacker may be able to share items from the lock screen.
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Analysis
by VulDB Data Team • 11/27/2020
The vulnerability described in CVE-2018-4428 represents a significant security flaw in iOS lock screen functionality that allowed unauthorized access to sharing capabilities on locked devices. This issue falls under the category of privilege escalation and unauthorized access, where a local attacker could exploit the lock screen interface to perform actions typically restricted to authenticated users. The flaw specifically affected the sharing function, which is a core feature in mobile operating systems that enables users to quickly share content across applications and services. The vulnerability was particularly concerning because it bypassed fundamental security boundaries that should prevent access to sensitive functions when a device is locked, creating a potential attack vector for malicious actors to access and share data without proper authentication.
The technical implementation of this vulnerability involved a misconfiguration in the lock screen security model that failed to properly restrict access to the share function when the device was secured. This type of flaw is classified as a security boundary violation, where the operating system failed to maintain proper access controls between the locked state and the available user interface functions. The issue demonstrates a failure in the principle of least privilege, where the system should have restricted access to sharing capabilities until proper authentication occurred. The vulnerability could be exploited through simple interaction with the lock screen interface, requiring no specialized tools or complex attack vectors, making it particularly dangerous for end users who might not be aware of the security implications.
The operational impact of this vulnerability extends beyond simple unauthorized access to encompass potential data leakage and privacy violations. When an attacker can share content from a locked device, they gain access to any information that was visible on the screen or accessible through the sharing function, potentially including sensitive documents, messages, photos, or other personal data. This represents a direct violation of the confidentiality and integrity principles outlined in the CIA triad, as unauthorized parties can access and disseminate information that should remain protected. The vulnerability also impacts the user's trust in the device's security model and could enable more sophisticated attacks where attackers use the sharing function as a stepping stone to access additional device features or data.
Mitigation strategies for this vulnerability include implementing proper access controls at the lock screen level, ensuring that sharing functions are completely disabled or restricted until proper authentication occurs. The fix implemented in iOS 12.1.1 addressed this by modifying the lock screen behavior to prevent access to sharing capabilities, which aligns with the ATT&CK framework's concept of privilege escalation and credential access. Organizations should also consider implementing additional security measures such as device encryption, secure lock screen configurations, and user education about the risks of leaving devices unlocked. This vulnerability highlights the importance of comprehensive security testing of user interface components and the need to ensure that all security boundaries are properly enforced, particularly in mobile environments where devices are frequently accessed in public or unsecured locations. The fix demonstrates how addressing lock screen security issues requires careful consideration of all available functions and their potential for exploitation, reinforcing the need for robust security architecture that considers both technical implementation and user experience tradeoffs.