CVE-2021-0688 in Android
Summary
by MITRE • 10/06/2021
In lockNow of PhoneWindowManager.java, there is a possible lock screen bypass due to a race condition. This could lead to local escalation of privilege with User execution privileges needed. User interaction is not needed for exploitation.Product: AndroidVersions: Android-10 Android-11 Android-8.1 Android-9Android ID: A-161149543
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Analysis
by VulDB Data Team • 10/10/2021
The vulnerability identified as CVE-2021-0688 represents a critical race condition flaw within the Android lock screen implementation that affects multiple Android versions including Android 8.1, 9, 10, and 11. This issue resides in the lockNow method of the PhoneWindowManager.java component, which governs the behavior of the lock screen and screen locking mechanisms. The race condition occurs during the transition between screen states, creating a temporal window where the system's security controls can be circumvented. The vulnerability is categorized under CWE-362, which specifically addresses race conditions that can lead to security flaws, and aligns with ATT&CK technique T1068, which covers local privilege escalation through system vulnerabilities. The flaw exploits a timing discrepancy in how the system handles lock screen transitions, allowing an attacker to potentially bypass the lock screen authentication mechanisms.
The technical implementation of this vulnerability stems from improper synchronization mechanisms within the lock screen management code. When the system attempts to lock the screen, a race condition can occur between the screen state transition and the authentication verification process. During this brief window, an attacker with user-level execution privileges can manipulate the system state to bypass the normal authentication flow. The vulnerability does not require user interaction for exploitation, making it particularly dangerous as it can be triggered automatically through system processes or malicious applications. The race condition manifests when multiple threads or processes attempt to access the lock screen state simultaneously, creating inconsistent system behavior where authentication checks may be bypassed or delayed.
The operational impact of this vulnerability extends to local privilege escalation scenarios where an attacker can gain elevated system privileges without proper authentication. While the initial exploitation requires user execution privileges, the successful bypass of the lock screen can lead to full system access, potentially allowing attackers to read sensitive data, modify system configurations, or install malicious software. The vulnerability affects the fundamental security model of Android devices, as it undermines the core lock screen protection mechanism that is designed to prevent unauthorized access to device resources. Security researchers have noted that this flaw could be particularly dangerous in enterprise environments where devices may contain sensitive corporate data, as it could allow attackers to access confidential information without proper authentication.
Mitigation strategies for CVE-2021-0688 should prioritize immediate system updates from device manufacturers and Google, as this vulnerability affects core Android security components. Organizations should implement comprehensive device management policies that enforce automatic security updates and monitor for unauthorized modifications to system components. The Android security team has addressed this issue through patch updates that correct the synchronization issues in the PhoneWindowManager.java implementation, requiring proper locking mechanisms to prevent concurrent access during screen state transitions. Network administrators should also consider implementing additional security controls such as device encryption, application whitelisting, and monitoring for suspicious system behavior that could indicate exploitation attempts. The vulnerability highlights the importance of proper race condition handling in security-critical code and serves as a reminder of the need for rigorous security testing of system-level components.