CVE-2016-0848 in Android
Summary
by MITRE
Race condition in Download Manager in Android 4.x before 4.4.4, 5.0.x before 5.0.2, 5.1.x before 5.1.1, and 6.x before 2016-04-01 allows attackers to bypass private-storage file-access restrictions via a crafted application that changes a symlink target, as demonstrated by obtaining Signature or SignatureOrSystem access, aka internal bug 26211054.
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Analysis
by VulDB Data Team • 07/12/2022
The vulnerability identified as CVE-2016-0848 represents a critical race condition within Android's Download Manager component that affects multiple versions of the Android operating system. This flaw exists in Android versions 4.x prior to 4.4.4, 5.0.x prior to 5.0.2, 5.1.x prior to 5.1.1, and 6.x prior to the 2016-04-01 security update. The vulnerability stems from improper handling of symbolic link operations during file download processes, creating a window where malicious applications can manipulate the system's file access controls. The race condition occurs when the Download Manager processes file operations concurrently with symlink modifications, allowing attackers to exploit timing discrepancies in the system's permission checking mechanisms.
The technical exploitation of this vulnerability involves a sophisticated attack pattern where an attacker crafts a malicious application that specifically targets the Download Manager's symlink handling behavior. During the download process, the attacker's application rapidly changes the target of a symbolic link while the Download Manager is processing the file transfer. This manipulation enables the attacker to bypass normal private storage file access restrictions that should normally prevent unauthorized access to system-level files. The vulnerability is particularly dangerous because it can be exploited to gain Signature or SignatureOrSystem level access privileges, which represent the highest levels of Android application permissions and provide extensive system-level capabilities.
The operational impact of CVE-2016-0848 extends beyond simple file access bypass to potentially compromise entire Android device security models. When successfully exploited, the vulnerability allows attackers to access files and resources that should be restricted to system-level applications or those with specific signature-based permissions. This represents a significant escalation of privileges that can enable further exploitation activities including but not limited to system modification, data exfiltration, and persistent backdoor installation. The vulnerability's exploitation is particularly concerning because it leverages legitimate system components rather than requiring root access or specialized exploitation techniques, making it more accessible to attackers with moderate technical capabilities. The race condition nature of the vulnerability means that successful exploitation relies on precise timing and concurrent system operations, which makes it challenging to detect through standard security monitoring approaches.
Security mitigations for CVE-2016-0848 primarily involve applying the relevant Android security patches released by Google as part of their regular security update cycle. Organizations and individuals should ensure that all affected Android devices receive the necessary updates, particularly those released prior to April 2016. The fix addresses the race condition by implementing proper synchronization mechanisms around symlink operations during download processing, ensuring that file access permissions are consistently enforced regardless of concurrent operations. From a defensive perspective, system administrators should implement comprehensive mobile device management policies that enforce timely security updates and monitor for unauthorized application installations that may attempt similar exploitation techniques. The vulnerability aligns with CWE-367, which addresses Time-of-Check to Time-of-Use (TOCTOU) race conditions, and represents a specific implementation weakness in Android's permission model that could be categorized under ATT&CK technique T1068, which covers "Exploitation for Privilege Escalation" and potentially T1547.001 for "Registry Run Keys / Startup Folder" if the exploitation leads to persistence mechanisms.
This vulnerability demonstrates the critical importance of proper synchronization and race condition handling in mobile operating systems, particularly in components that interact with file systems and permission models. The flaw highlights how seemingly minor implementation details in system components can create significant security risks when concurrent operations are not properly coordinated. The vulnerability also underscores the need for comprehensive security testing of system-level components, particularly those involved in file handling and access control mechanisms. Organizations should maintain robust patch management processes specifically for mobile platforms, as the window of vulnerability for this issue was significant and affected multiple Android versions. The exploitation techniques used in this vulnerability represent a common pattern in mobile security where attackers leverage legitimate system functionality to bypass security controls, making traditional security measures less effective against such sophisticated attacks.