CVE-2021-0645 in Android
Summary
by MITRE • 08/17/2021
In shouldBlockFromTree of ExternalStorageProvider.java, there is a possible permissions bypass. This could lead to local escalation of privilege, allowing an app to read private app directories in external storage, which should be restricted in Android 11, with no additional execution privileges needed. User interaction is needed for exploitation.Product: AndroidVersions: Android-11Android ID: A-157320644
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Analysis
by VulDB Data Team • 08/20/2021
The vulnerability identified as CVE-2021-0645 resides within the ExternalStorageProvider.java component of Android 11 systems, specifically in the shouldBlockFromTree method implementation. This flaw represents a critical permissions bypass that undermines the security model designed to protect private application directories stored on external storage devices. The vulnerability manifests as a local privilege escalation vector that allows malicious applications to bypass the intended restrictions on accessing other applications' private data directories, effectively compromising the principle of least privilege that governs Android's security architecture.
The technical implementation of this vulnerability stems from improper validation within the shouldBlockFromTree method which is responsible for determining whether certain file system operations should be blocked based on access permissions and security contexts. When an application attempts to access external storage directories, the method fails to properly enforce the security boundaries that should prevent one application from accessing another application's private storage areas. This flaw operates at the system level where the external storage provider component should act as a gatekeeper for all external storage access requests, but instead allows unauthorized access to sensitive data that should remain isolated between applications.
From an operational perspective, this vulnerability enables a malicious application to read private data from other applications stored on external storage, which represents a significant compromise of user privacy and application security. The attack requires only user interaction for initial exploitation, as the malicious app would need to be installed and executed by the user, but once operational it can access all private application directories on external storage without requiring additional privileges or root access. This means that even applications with minimal permissions can potentially access sensitive data such as database files, configuration settings, cached data, and other private application resources that should remain protected from unauthorized access.
The security implications extend beyond simple data theft to include potential information disclosure, privacy violations, and possible further exploitation opportunities. Attackers could leverage this vulnerability to gather sensitive user information, access application-specific data that may contain authentication tokens, personal identifiers, or other confidential information. The vulnerability affects the core Android security model's enforcement of external storage access controls, specifically targeting the storage access framework that was designed to provide granular control over external storage permissions in Android 11. This issue represents a failure in the Android security model's enforcement mechanisms and could potentially allow for more sophisticated attacks if combined with other vulnerabilities or if the attacker can manipulate the user into granting additional permissions.
Mitigation strategies for CVE-2021-0645 should focus on immediate system updates and security configuration adjustments. Android security patches released by Google address this vulnerability by correcting the permission validation logic within the ExternalStorageProvider component, ensuring that proper access controls are enforced when applications attempt to access external storage directories. Organizations and users should prioritize applying the relevant security updates from their device manufacturers as soon as possible, as this vulnerability could be exploited to gain unauthorized access to sensitive application data. Additionally, users should exercise caution when installing applications from untrusted sources, as these malicious applications could exploit this vulnerability to access private data from other applications on the device. The vulnerability aligns with CWE-284 (Improper Access Control) and could potentially be leveraged as part of broader attack chains in the MITRE ATT&CK framework, specifically under techniques related to privilege escalation and credential access.