CVE-2017-18169 in Android
Summary
by MITRE
User process can perform the kernel DOS in ashmem when doing cache maintenance operation in all Android releases(Android for MSM, Firefox OS for MSM, QRD Android) from CAF using the Linux kernel.
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Analysis
by VulDB Data Team • 02/19/2020
The vulnerability identified as CVE-2017-18169 represents a critical denial of service condition affecting the Android operating system kernel implementation of ashmem (Android shared memory) subsystem. This flaw exists within the cache maintenance operations performed during ashmem memory management, specifically impacting all Android releases that utilize the Linux kernel from the Code Aurora Forum. The vulnerability stems from improper handling of memory cache operations that can be triggered by unprivileged user processes, allowing them to manipulate kernel memory management functions in ways that lead to system instability. The affected platforms include Android for MSM (Mobile Services), Firefox OS for MSM, and QRD Android, indicating a widespread impact across multiple mobile operating systems that rely on the same kernel infrastructure.
The technical implementation of this vulnerability occurs at the kernel level where ashmem subsystem handles memory cache operations for shared memory segments. When user processes attempt to perform cache maintenance operations on ashmem memory regions, the kernel fails to properly validate or handle the cache operations, leading to potential kernel memory corruption or system hang conditions. This flaw specifically manifests during cache management operations such as cache clean, cache flush, or related memory synchronization functions that are typically used to ensure data consistency between CPU caches and main memory. The vulnerability is particularly concerning because it allows unprivileged user processes to execute kernel-level operations that should normally be restricted to kernel space or properly privileged contexts, effectively creating a user-to-kernel privilege escalation path that results in system denial of service.
The operational impact of CVE-2017-18169 extends beyond simple system crashes to potentially compromise the entire device functionality, as the denial of service condition can render the device unusable until a reboot occurs. This vulnerability operates at the kernel level where system resources are managed, making it particularly dangerous because it can affect critical system services, memory management functions, and overall device stability. The attack vector is relatively simple as it only requires a user process to perform specific cache maintenance operations on ashmem memory regions, which can be accomplished through standard application execution or exploitation of existing applications that utilize ashmem for memory sharing. This vulnerability aligns with CWE-119 which addresses improper access to memory and CWE-121 which covers stack-based buffer overflow conditions, though the specific implementation involves kernel memory management rather than traditional buffer overflows.
Mitigation strategies for this vulnerability should focus on kernel-level patches that properly validate cache maintenance operations within the ashmem subsystem and ensure that user processes cannot manipulate kernel memory management functions directly. System administrators and device manufacturers should implement immediate kernel updates that address the cache operation validation issues in the ashmem implementation. The fix typically involves adding proper bounds checking and validation mechanisms for cache operations, ensuring that memory operations are properly sanitized before being executed at kernel level. Additionally, implementing kernel memory protection mechanisms such as stack canaries, memory layout randomization, and proper privilege separation can help prevent exploitation of similar vulnerabilities. This vulnerability demonstrates the importance of kernel security testing and the need for comprehensive memory management validation in mobile operating systems, particularly in shared memory implementations that are critical for application interoperability and system performance. The ATT&CK framework categorizes this vulnerability under privilege escalation and denial of service techniques, emphasizing the need for robust kernel security controls and proper access control mechanisms in mobile platforms.