CVE-2018-21086 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 double free in vnswap_init_backing_storage. The Samsung ID is SVE-2017-11177 (February 2018).
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Analysis
by VulDB Data Team • 10/09/2020
The vulnerability CVE-2018-21086 represents a critical race condition flaw affecting Samsung mobile devices running on Linux kernel versions 5.x, 6.0, and 7.x. This issue manifests within the vnswap_init_backing_storage function, which is responsible for initializing backing storage for virtual memory swap operations. The race condition occurs when multiple threads or processes attempt to access and modify the same memory resources simultaneously without proper synchronization mechanisms, creating a window of opportunity for malicious exploitation. The vulnerability was identified and tracked by Samsung under the internal identifier SVE-2017-11177, with the disclosure occurring in February 2018, highlighting the extended timeline between discovery and public reporting that often characterizes mobile security vulnerabilities.
The technical implementation of this double free vulnerability stems from improper handling of memory allocation and deallocation sequences within the virtual memory management subsystem. When the vnswap_init_backing_storage function processes concurrent access requests, it fails to maintain proper atomicity in its operations, allowing a malicious actor to manipulate the memory state such that a single memory block gets freed twice. This double free condition creates a predictable memory corruption scenario where an attacker can potentially overwrite critical data structures or execute arbitrary code. The vulnerability aligns with CWE-415, which specifically addresses double free conditions in memory management, and represents a classic example of how concurrent access controls fail in kernel-level implementations. The underlying architecture of Android's memory management system, particularly its integration with Linux kernel swap mechanisms, provides the necessary environment for this race condition to manifest.
The operational impact of CVE-2018-21086 extends beyond simple system instability to potentially enable full system compromise on affected Samsung devices. Mobile devices running vulnerable software versions become susceptible to privilege escalation attacks where an attacker could gain elevated system privileges through controlled manipulation of the memory management subsystem. The vulnerability affects devices that rely on the Linux kernel's virtual memory swap functionality, which is fundamental to Android's memory management and application performance optimization. Attackers could exploit this condition to execute malicious code with kernel-level privileges, potentially leading to complete device compromise, data exfiltration, or persistent backdoor installation. The vulnerability's presence in multiple Android versions (5.x, 6.0, and 7.x) indicates it was likely introduced in a core kernel component that remained unchanged across these releases, making it particularly concerning for the large user base of affected devices.
Mitigation strategies for CVE-2018-21086 primarily focus on immediate device updates and system hardening measures. Samsung released security patches addressing this vulnerability through official software updates, which users should install immediately to protect their devices. System administrators and security professionals should implement monitoring for suspicious memory allocation patterns and ensure that all affected devices receive the latest security patches. The vulnerability demonstrates the critical importance of proper synchronization mechanisms in kernel-level code, particularly in memory management functions that handle concurrent access. Organizations should also consider implementing device management policies that enforce automatic security updates and maintain inventory of affected devices. From an ATT&CK framework perspective, this vulnerability would map to techniques involving privilege escalation and kernel exploitation, making it a significant concern for mobile threat hunting and incident response activities. The vulnerability underscores the necessity for comprehensive security testing of kernel components, particularly those handling concurrent memory operations, and highlights the importance of adhering to secure coding practices that prevent race conditions in multi-threaded environments.