CVE-2021-39748 in Android
Summary
by MITRE • 03/30/2022
In InputMethodEditor, there is a possible way to access some files accessible to Settings due to an unsafe PendingIntent. 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-203777141
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Analysis
by VulDB Data Team • 04/02/2022
The vulnerability identified as CVE-2021-39748 resides within the InputMethodEditor component of Android 12L systems, representing a significant security flaw that enables unauthorized file access through improperly configured PendingIntent mechanisms. This issue stems from the insecure handling of inter-process communication elements that should normally maintain strict access controls between system components. The vulnerability specifically affects the Settings application's ability to control file access through the InputMethodEditor, creating an unexpected pathway for information disclosure that bypasses normal security boundaries. The flaw demonstrates a clear failure in the Android security model's principle of least privilege, where the InputMethodEditor component inadvertently exposes file system access to entities that should not possess such capabilities.
The technical root cause of this vulnerability lies in the improper construction of PendingIntent objects within the InputMethodEditor implementation, which creates unsafe references that can be exploited by malicious applications or system components. This unsafe PendingIntent construction allows for the creation of indirect access pathways to files that are normally restricted to the Settings application, effectively breaking the security isolation that should exist between different system components. The vulnerability manifests through the manipulation of PendingIntent flags and intent parameters that should normally enforce strict access controls and prevent unauthorized cross-component file access. This type of flaw commonly maps to CWE-264, which addresses permissions, privileges, and access controls, specifically highlighting weaknesses in how system-level components manage inter-process communication security boundaries.
The operational impact of this vulnerability is significant as it enables local information disclosure without requiring any additional execution privileges or user interaction for exploitation. Attackers can leverage this vulnerability to access sensitive files that are typically restricted to the Settings application, potentially exposing system configuration data, user preferences, or other confidential information. The lack of user interaction requirements makes this vulnerability particularly dangerous as it can be exploited automatically without any user awareness or consent. This type of information disclosure threat aligns with ATT&CK technique T1005, which focuses on data from local system repositories, and represents a clear violation of the Android security model's fundamental access control mechanisms. The vulnerability essentially creates a backdoor pathway that allows unauthorized components to read files that should be protected by the system's permission model.
Mitigation strategies for this vulnerability should focus on proper PendingIntent construction and implementation of strict access control measures within the InputMethodEditor component. Android developers should ensure that all PendingIntent objects are properly configured with appropriate flags and security parameters that prevent unauthorized access to system resources. The fix should involve implementing proper intent filtering and access control checks that validate the identity and permissions of requesting components before granting file system access. Security hardening measures should include the removal of unnecessary PendingIntent flags that could create unsafe access pathways and the implementation of more restrictive permission models for inter-component communication. Additionally, regular security audits of system components should be conducted to identify and remediate similar unsafe PendingIntent usage patterns that could create analogous vulnerabilities. The vulnerability also emphasizes the importance of following Android security best practices for intent handling and component communication, particularly in system-level applications where security boundaries are most critical.