CVE-2018-9422 in Android
Summary
by MITRE
In get_futex_key of futex.c, there is a use-after-free due to improper locking. This could lead to local escalation of privilege with no additional privileges needed. User interaction is not needed for exploitation. Product: Android Versions: Android kernel Android ID: A-74250718 References: Upstream kernel.
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Analysis
by VulDB Data Team • 09/13/2024
The vulnerability identified as CVE-2018-9422 represents a critical use-after-free condition within the Android kernel's futex implementation, specifically in the get_futex_key function of the futex.c file. This flaw resides in the kernel's synchronization mechanisms that manage futexes, which are fundamental building blocks for implementing mutexes, semaphores, and other locking primitives in the Linux kernel. The issue stems from improper locking protocols during the processing of futex operations, creating a window where memory that has been freed can still be accessed by subsequent operations.
The technical exploitation of this vulnerability occurs through a race condition scenario where the kernel fails to properly acquire locks before accessing futex key structures. When multiple threads or processes attempt to access the same futex object concurrently, the lack of proper synchronization allows one thread to free a memory structure while another thread attempts to reference it, leading to a use-after-free condition. This type of vulnerability falls under CWE-416, which specifically addresses the use of freed memory, and is particularly dangerous in kernel contexts where such flaws can be leveraged for privilege escalation.
The operational impact of CVE-2018-9422 is severe as it enables local privilege escalation without requiring any special privileges or user interaction. An attacker with normal user-level access can exploit this vulnerability to gain elevated privileges, potentially leading to full system compromise. The vulnerability affects Android kernel versions and is particularly concerning because it operates entirely within kernel space, making it difficult to detect and mitigate through traditional user-space security measures. The Android ID A-74250718 indicates this was tracked by Google's security team and represents a significant threat to Android device security.
The exploitation process typically involves creating a specific race condition scenario where the attacker can control the timing of memory allocation and deallocation operations. This allows the attacker to manipulate the futex key structures in such a way that freed memory can be reused and accessed by malicious code. The lack of user interaction requirement makes this vulnerability particularly dangerous as it can be exploited automatically without any need for social engineering or user deception. This aligns with ATT&CK technique T1068, which covers 'Local Privilege Escalation' through kernel vulnerabilities, and demonstrates how kernel-level flaws can be leveraged to bypass traditional security controls.
Mitigation strategies for CVE-2018-9422 primarily involve applying the upstream kernel patches that address the improper locking mechanisms in the futex implementation. Android device manufacturers should prioritize updating their kernel versions to include the fix that properly implements locking protocols around futex key access. System administrators should monitor for security updates from their device vendors and apply patches promptly, as the vulnerability can be exploited in the wild without user interaction. Additionally, kernel hardening techniques such as stack canaries, memory protection mechanisms, and kernel address space layout randomization can provide additional defense-in-depth measures against exploitation attempts. The vulnerability highlights the importance of proper synchronization in kernel code and the critical need for thorough testing of concurrent access scenarios in system-level programming.