CVE-2016-3838 in Android
Summary
by MITRE
Android 6.x before 2016-08-01 allows attackers to cause a denial of service (loss of locked-screen 911 functionality) via a crafted application that uses the app-pinning feature, aka internal bug 28761672.
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Analysis
by VulDB Data Team • 03/19/2019
This vulnerability affects android 6.x operating systems prior to the 2016-08-01 security update and represents a significant denial of service weakness that specifically targets the locked-screen 911 functionality. The flaw manifests when a malicious application exploits the app-pinning feature to manipulate the device's screen locking behavior, resulting in complete loss of access to emergency services functionality that users rely upon during critical situations. The vulnerability is particularly concerning because it directly impacts life-saving emergency services availability, as the 911 functionality becomes inaccessible when the device is locked.
The technical implementation of this vulnerability leverages the app-pinning feature that was introduced in android 6.0 to allow applications to remain in the foreground when users navigate away from them. Attackers can craft malicious applications that abuse this functionality to prevent the system from properly handling the locked-screen state, specifically interfering with how the emergency dialer operates. This manipulation occurs through improper handling of system-level permissions and foreground service management that controls how applications interact with the device's lock screen. The vulnerability resides in the operating system's core lock screen management and emergency service handling mechanisms, where the app-pinning feature creates an unintended interaction that compromises the security model.
The operational impact of this vulnerability extends beyond simple functionality degradation, as it creates a critical risk to user safety and emergency response capabilities. When the locked-screen 911 functionality is compromised, users cannot access emergency services during device lock states, which represents a serious failure in the device's security and emergency response design. The attack requires only a malicious application to be installed and executed, making it particularly dangerous as it can be deployed through standard app distribution channels or social engineering tactics. This vulnerability directly violates the principle of least privilege and fails to maintain proper isolation between emergency services and regular application functionality, creating a dangerous security gap in the android operating system's design.
Organizations and users should implement immediate mitigations including updating to android 6.x versions released after 2016-08-01, which contain the necessary patches to address the app-pinning interaction with lock screen functionality. System administrators should conduct comprehensive security assessments of all android devices within their environment, particularly focusing on emergency services availability and lock screen behavior. The vulnerability aligns with CWE-284 access control weaknesses and represents a failure in the operating system's security model that could be classified under ATT&CK technique T1499 for denial of service attacks. Additionally, this vulnerability demonstrates the importance of proper privilege separation between emergency services and regular applications, as well as the need for comprehensive testing of system features that interact with security-critical functionality such as emergency dialers and lock screen management.