CVE-2021-0973 in Android
Summary
by MITRE • 12/15/2021
In isFileUri of UriUtil.java, there is a possible way to bypass ignoring file://URI attachment due to improper handling of case sensitivity. This could lead to local information disclosure with no additional execution privileges needed. User interaction is needed for exploitation.Product: AndroidVersions: Android-12Android ID: A-197328178
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Analysis
by VulDB Data Team • 12/18/2021
The vulnerability identified as CVE-2021-0973 resides within the Android operating system's UriUtil.java file, specifically in the isFileUri method implementation. This flaw represents a critical security issue that stems from improper case sensitivity handling when processing file:// URI attachments. The vulnerability affects Android 12 and is tracked under Android ID A-197328178, demonstrating the system's failure to properly validate URI schemes during file access operations.
The technical flaw manifests when the Android system processes file:// URIs that contain uppercase characters in their scheme specification. The isFileUri method fails to normalize the URI scheme comparison, allowing attackers to bypass intended security restrictions that should prevent file:// URI attachments from being processed. This improper handling creates a condition where the system incorrectly identifies certain URI formats as valid file access requests, even when they should be ignored for security reasons. The vulnerability specifically impacts how the system determines whether a URI represents a file:// scheme, enabling a bypass of the intended file URI filtering mechanism.
From an operational perspective, this vulnerability enables local information disclosure without requiring any additional execution privileges or user interaction beyond the initial triggering condition. The attack vector requires only that a malicious actor present a specially crafted file:// URI with uppercase characters in the scheme, which then gets processed through the vulnerable method. This allows unauthorized access to local file system resources that should normally be restricted. The impact extends to all applications running on affected Android versions, as the vulnerability exists at the core URI handling layer of the operating system.
The security implications of this vulnerability align with CWE-20, "Improper Input Validation," and can be mapped to ATT&CK technique T1059.007 for executing commands through file URI manipulation. The flaw creates a pathway for information disclosure that could potentially expose sensitive user data stored locally on the device, including personal documents, application data, and other file system resources. Organizations and users should be particularly concerned about this vulnerability as it operates at the system level and can be exploited without requiring elevated privileges or complex attack chains.
Effective mitigations for this vulnerability include applying the latest Android security patches provided by Google, which address the case sensitivity handling in the URI processing logic. System administrators should also implement monitoring for unusual file URI access patterns and consider restricting file URI handling in applications where possible. The fix typically involves normalizing URI schemes to lowercase before comparison operations, ensuring that file:// URIs are consistently identified regardless of case variations in the scheme specification. Additionally, users should avoid opening untrusted files or links that might contain malformed URI references, particularly in email attachments or web content that could trigger this vulnerability.