CVE-2021-0476 in Android
Summary
by MITRE • 06/11/2021
In FindOrCreatePeer of btif_av.cc, there is a possible use after free due to a race condition. This could lead to local escalation of privilege with no additional execution privileges needed. User interaction is not needed for exploitation.Product: AndroidVersions: Android-11 Android-9 Android-10Android ID: A-169252501
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Analysis
by VulDB Data Team • 06/14/2021
The vulnerability identified as CVE-2021-0476 resides within the Bluetooth subsystem of Android operating systems, specifically in the btif_av.cc source file where the FindOrCreatePeer function exhibits a use-after-free condition. This flaw stems from a race condition that occurs during concurrent access to shared memory resources, creating a window of opportunity for malicious code to exploit the temporal gap between object deallocation and subsequent memory reuse. The vulnerability affects multiple Android versions including Android 11, Android 9, and Android 10, indicating a widespread impact across the Android ecosystem.
The technical nature of this vulnerability places it squarely within CWE-416, which categorizes use-after-free conditions as a critical memory safety issue. The race condition in btif_av.cc allows for a scenario where a Bluetooth peer connection object is freed from memory while another thread or process attempts to access it, leading to unpredictable behavior and potential code execution. The Bluetooth interface layer in Android is particularly sensitive to such timing issues since it handles concurrent operations between multiple Bluetooth devices and system components. The flaw manifests when the FindOrCreatePeer function fails to properly synchronize access to peer connection objects, creating a situation where freed memory can be accessed and manipulated.
From an operational perspective, this vulnerability represents a significant local privilege escalation vector that requires no additional execution privileges beyond normal user access. The exploitation process leverages the inherent timing vulnerability in the Bluetooth subsystem to overwrite memory contents with malicious data, potentially allowing attackers to execute arbitrary code with elevated privileges. The lack of user interaction requirement makes this vulnerability particularly dangerous as it can be exploited automatically without user consent or awareness. The attack surface is broadened by the fact that Bluetooth functionality is typically enabled by default on Android devices, providing persistent access points for exploitation.
The security implications extend beyond simple privilege escalation to encompass potential system compromise and data exposure. Attackers could leverage this vulnerability to gain root access to affected devices, enabling them to modify system files, install malicious applications, or exfiltrate sensitive data. The Android security model relies heavily on proper memory management and synchronization mechanisms to prevent such scenarios, making this race condition particularly concerning. Mitigation strategies should focus on implementing proper memory synchronization primitives and ensuring that all shared resources are properly protected against concurrent access. The vulnerability highlights the critical importance of secure coding practices in system-level components, particularly those handling hardware interfaces like Bluetooth. Organizations should prioritize patching affected Android versions and consider implementing additional runtime protections to prevent exploitation of similar timing-based vulnerabilities in other system components.