CVE-2018-21085 in Samsung
Summary
by MITRE
An issue was discovered on Samsung mobile devices with L(5.x), M(6.0), and N(7.x) software. There is a race condition with a resultant use-after-free in vnswap_deinit_backing_storage. The Samsung ID is SVE-2017-11176 (February 2018).
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Analysis
by VulDB Data Team • 10/09/2020
The vulnerability identified as CVE-2018-21085 represents a critical race condition flaw affecting Samsung mobile devices running on Linux-based operating systems version 5.x (Lollipop), 6.0 (Marshmallow), and 7.x (Nougat). This issue manifests within the vnswap_deinit_backing_storage function, which is part of the kernel-level memory management subsystem responsible for handling virtual memory swap operations. The race condition occurs during the deinitialization process of backing storage for virtual memory swap areas, creating a window where concurrent access patterns can lead to improper memory state management. The vulnerability was catalogued under Samsung's internal tracking system as SVE-2017-11176 and was publicly disclosed in February 2018, highlighting the inherent complexity of kernel-level memory management operations on mobile platforms.
The technical flaw stems from improper synchronization mechanisms within the vnswap_deinit_backing_storage function, which handles cleanup operations for virtual memory swap backing storage. When multiple threads or processes attempt to access or modify the same memory resources simultaneously during the deinitialization phase, the race condition allows for a use-after-free scenario to occur. This particular vulnerability falls under CWE-362, which specifically addresses Race Conditions, and more precisely maps to CWE-416, Use After Free, as the end result of the race condition leads to memory being accessed after it has been freed. The flaw exploits the timing gap between when memory is freed and when it is actually reused or accessed by other system processes, creating an exploitable state where malicious code could potentially manipulate the freed memory or cause system instability.
The operational impact of CVE-2018-21085 extends beyond simple system instability, potentially enabling privilege escalation and arbitrary code execution on affected Samsung devices. Mobile platforms running these vulnerable software versions could be compromised through carefully crafted attacks that exploit the race condition during memory management operations. The vulnerability's exploitation could allow attackers to gain elevated privileges within the kernel space, potentially leading to complete system compromise. This risk is particularly significant for mobile devices where the kernel serves as the core security boundary between user applications and system-level operations. The vulnerability affects a substantial number of Samsung devices that were shipped with these Android versions, making it a widespread concern for device security and user privacy across the Samsung ecosystem.
Mitigation strategies for CVE-2018-21085 primarily involve applying official security patches released by Samsung and Google as part of their regular security updates. Users should ensure their devices receive the latest security updates, particularly those addressing kernel-level vulnerabilities in the Android operating system. System administrators and security teams should implement comprehensive patch management protocols to ensure all affected devices receive timely updates. Additional protective measures include monitoring for suspicious memory access patterns and implementing runtime integrity checks that can detect anomalous behavior associated with use-after-free conditions. The vulnerability demonstrates the critical importance of proper synchronization mechanisms in kernel code and highlights the need for thorough security testing of memory management functions, particularly those handling concurrent access scenarios. Organizations should also consider implementing device-level security controls such as kernel address space layout randomization and other exploit mitigation techniques to reduce the effectiveness of potential exploitation attempts.