CVE-2021-39766 in Android
Summary
by MITRE • 03/30/2022
In Settings, there is a possible way to determine whether an app is installed, without query permissions, due to side channel information disclosure. This could lead to local information disclosure with no additional execution privileges needed. User interaction is not needed for exploitation.Product: AndroidVersions: Android-12LAndroid ID: A-198296421
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Analysis
by VulDB Data Team • 04/02/2022
This vulnerability exists within the Android Settings application and represents a significant information disclosure flaw that undermines user privacy and system security. The issue stems from the improper handling of side channel information that allows attackers to infer the presence of specific applications on a device without requiring any special permissions or user interaction. The vulnerability is particularly concerning because it operates at the system level within the Settings framework, making it accessible to any malicious application or attacker with basic system access. This type of information leakage creates a pathway for adversaries to gather intelligence about installed applications, which can be used for further exploitation or targeted attacks.
The technical root cause of CVE-2021-39766 lies in the way Android Settings processes and responds to queries related to application availability. When an application attempts to determine whether another app is installed, the system's response timing or behavioral patterns inadvertently reveal information about the target application's existence. This side channel attack exploits the subtle differences in system response times or memory access patterns that occur when checking for installed applications versus non-existent ones. The vulnerability specifically affects Android 12L and represents a flaw in the permission model where no query permissions are required to exploit this information disclosure mechanism. This aligns with CWE-203, which describes the disclosure of information through side channels, and demonstrates how system-level inconsistencies can create exploitable attack vectors.
The operational impact of this vulnerability extends beyond simple information gathering, as it enables sophisticated reconnaissance attacks that can be used to build comprehensive profiles of target devices. Attackers can leverage this information to identify potential targets for more serious exploits, such as privilege escalation attacks or targeted malware delivery. The vulnerability requires no additional execution privileges or user interaction, making it particularly dangerous as it can be exploited silently in the background. This characteristic places it within the ATT&CK framework under the technique T1083 (File and Directory Discovery) and potentially T1592 (Gather Victim Host Information) as it allows for systematic enumeration of installed applications. The lack of user interaction requirements means that this vulnerability can be exploited continuously without detection, creating a persistent threat vector.
Mitigation strategies for CVE-2021-39766 should focus on strengthening the permission model and implementing proper side channel resistance mechanisms within the Android Settings framework. System updates from Google should be applied immediately to address the underlying implementation flaws in how application presence checks are handled. Organizations should also consider implementing network-level monitoring to detect unusual patterns of application enumeration that might indicate exploitation attempts. The vulnerability highlights the importance of proper input validation and response handling in system-level applications, as well as the need for comprehensive security testing that includes side channel analysis. Additionally, developers should be aware of this vulnerability when creating applications that interact with system settings or perform application discovery operations, as they may need to implement additional safeguards to prevent exploitation of similar mechanisms in their own code.