CVE-2020-0479 in Android
Summary
by MITRE • 12/15/2020
In callUnchecked of DocumentsProvider.java, there is a possible permissions bypass. This could lead to local escalation of privilege allowing a malicious app to access files available to the DocumentProvider without user permission, with no additional execution privileges needed. User interaction is needed for exploitation.Product: AndroidVersions: Android-11Android ID: A-157294893
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Analysis
by VulDB Data Team • 12/18/2020
The vulnerability described in CVE-2020-0479 resides within the DocumentsProvider.java component of Android systems, specifically in the callUnchecked method implementation. This flaw represents a critical permissions bypass issue that undermines the fundamental security model of Android's document access architecture. The vulnerability affects Android 11 systems and is identified by Android ID A-157294893, demonstrating the severity of the issue within the platform's security framework.
The technical flaw manifests in how the callUnchecked method handles permission validation when processing document provider requests. This method is designed to allow certain operations to proceed without explicit user consent, but the implementation contains a logic error that permits unauthorized access to documents that should require user permission. The vulnerability operates at the system level where document providers typically mediate access between applications and files stored on external storage or shared locations. When an application invokes this method, it should normally require proper authorization tokens or user interaction to proceed, but the flaw allows bypassing these critical checks.
The operational impact of this vulnerability extends beyond simple data access, creating a potential pathway for local privilege escalation. A malicious application can exploit this flaw to gain unauthorized access to files that are normally restricted to specific applications or user contexts. This means that an attacker could potentially read, modify, or delete documents that should be protected by the DocumentProvider's permission model. The vulnerability is particularly concerning because it requires no additional execution privileges beyond what a standard application might already possess, making it accessible through ordinary app installation and execution. The need for user interaction suggests that while the attack requires some initial user engagement, the actual exploitation can occur without ongoing user involvement once the initial conditions are met.
This vulnerability aligns with CWE-284, which addresses improper access control issues, and represents a clear violation of the principle of least privilege in Android's security architecture. From an ATT&CK perspective, this flaw maps to privilege escalation techniques where adversaries can leverage system-level vulnerabilities to gain broader access rights. The attack surface includes any application that interacts with document providers or relies on the DocumentsProvider framework for file access operations. The implications are significant for user privacy and data protection, as this vulnerability could enable unauthorized access to sensitive documents, personal files, and potentially confidential business information stored in shared document provider contexts.
Mitigation strategies should focus on implementing proper input validation and access control checks within the DocumentsProvider implementation. System administrators and developers should ensure that all document provider operations require explicit authorization tokens and that the callUnchecked method properly validates the requesting application's permissions. Updates to the Android operating system should address the underlying logic error in the permission validation process. Additionally, application developers should review their document provider implementations to ensure they properly enforce access controls and do not inadvertently expose sensitive data through improper method calls. The vulnerability underscores the importance of rigorous security testing for system-level components that handle sensitive data access operations and the necessity of maintaining up-to-date security patches to protect against known vulnerabilities in core platform components.