CVE-2016-5340 in Android
Summary
by MITRE
The is_ashmem_file function in drivers/staging/android/ashmem.c in a certain Qualcomm Innovation Center (QuIC) Android patch for the Linux kernel 3.x mishandles pointer validation within the KGSL Linux Graphics Module, which allows attackers to bypass intended access restrictions by using the /ashmem string as the dentry name.
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Analysis
by VulDB Data Team • 09/22/2022
The vulnerability identified as CVE-2016-5340 resides within the Linux kernel's Android-specific staging module, specifically in the drivers/staging/android/ashmem.c file. This flaw represents a critical security issue affecting Qualcomm's Android patches for kernel version 3.x, where the is_ashmem_file function fails to properly validate memory pointers during operations within the KGSL (Kernel Graphics Subsystem) Linux Graphics Module. The vulnerability stems from improper handling of dentry name validation, creating a pathway for unauthorized access to ashmem (anonymous shared memory) resources that should be restricted to legitimate processes.
The technical exploitation of this vulnerability occurs through a carefully crafted pointer validation bypass mechanism that allows attackers to manipulate the dentry name string to match the hardcoded "/ashmem" identifier. This manipulation enables unauthorized processes to access ashmem regions that are normally protected by kernel-level access controls, effectively circumventing the intended security boundaries that separate different application processes and system components. The flaw operates at the kernel level where memory management and process isolation should be strictly enforced, making it particularly dangerous as it undermines fundamental security principles of the operating system.
From an operational standpoint, this vulnerability presents significant risks to Android devices running affected kernel versions, as it allows attackers to potentially access sensitive memory regions that contain application data, system information, or graphics buffers. The impact extends beyond simple information disclosure, as it could enable privilege escalation attacks where malicious applications gain access to system-level resources that should remain protected. The vulnerability specifically affects the KGSL graphics subsystem which handles GPU operations and memory management, making it particularly concerning for devices with advanced graphics capabilities and multimedia processing requirements.
The security implications of CVE-2016-5340 align with CWE-125, which addresses out-of-bounds read vulnerabilities, and can be mapped to ATT&CK technique T1068, which covers "Exploitation for Privilege Escalation." The vulnerability's classification as a kernel-level pointer validation flaw makes it particularly dangerous because it operates below the application layer where typical security controls are implemented. Remediation efforts should focus on implementing proper pointer validation mechanisms within the is_ashmem_file function and ensuring that dentry name comparisons do not create exploitable conditions. Additionally, system administrators should prioritize updating to patched kernel versions that address this specific pointer validation bypass mechanism and implement comprehensive monitoring for unauthorized access attempts to ashmem resources.
This vulnerability demonstrates the complexity of kernel security and the critical importance of proper input validation even at the most fundamental levels of operating system implementation. The flaw represents a classic case of insufficient boundary checking that allows attackers to manipulate system state through carefully crafted inputs, highlighting the need for robust security testing of kernel modules and the importance of maintaining up-to-date security patches in mobile operating systems.