CVE-2017-9684 in Android
Summary
by MITRE
In all Qualcomm products with Android releases from CAF using the Linux kernel, a race condition in a USB driver can lead to a Use After Free condition.
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Analysis
by VulDB Data Team • 01/09/2021
The vulnerability identified as CVE-2017-9684 represents a critical race condition flaw within the USB driver implementation of Qualcomm Android products that utilize the Linux kernel. This issue affects all Qualcomm chipsets running Android versions through the Code Aurora Forum (CAF) framework, creating a widespread security concern across numerous mobile devices and embedded systems. The vulnerability stems from improper synchronization mechanisms within the USB subsystem, where concurrent access to shared resources occurs without adequate protection measures. This fundamental design flaw allows malicious actors to exploit temporal gaps in the driver's execution flow, potentially leading to system compromise through memory corruption attacks.
The technical implementation of this vulnerability manifests as a race condition in the USB driver's handling of device connection and disconnection events. When multiple threads or processes attempt to access USB resources simultaneously, the driver fails to properly serialize these operations, creating a window where freed memory locations may still be referenced by other processes. This Use After Free condition occurs because the driver allocates memory for USB device structures and subsequently frees them without ensuring that all pending references are cleared. The flaw specifically impacts the Linux kernel's USB subsystem implementation on Qualcomm platforms, where the race condition can be triggered through controlled USB enumeration sequences or malicious device connections that exploit the timing gaps in memory management.
The operational impact of CVE-2017-9684 extends beyond simple memory corruption, as it provides potential attack vectors for privilege escalation and system compromise. An attacker with physical access to a vulnerable device or the ability to establish malicious USB connections could leverage this vulnerability to execute arbitrary code with kernel-level privileges. The attack surface is particularly concerning given that USB interfaces are commonly used for device communication, charging, and data transfer, making exploitation relatively accessible. This vulnerability aligns with CWE-362, which specifically addresses race conditions in concurrent programming, and maps to ATT&CK technique T1059.007 for command and scripting interpreter usage, as successful exploitation could enable persistent access through kernel-level modifications. The vulnerability's presence in Qualcomm's CAF implementation means that devices from multiple manufacturers using these chipsets are potentially affected, creating a significant security risk across the mobile ecosystem.
Mitigation strategies for CVE-2017-9684 require both immediate patching and defensive programming approaches to address the underlying race condition. Device manufacturers should prioritize applying Qualcomm's security patches that implement proper mutex locking mechanisms and memory synchronization protocols within the USB driver. System administrators and security teams should monitor for unauthorized USB device connections and implement USB device whitelisting policies where possible. The fix typically involves adding proper synchronization primitives such as mutexes or semaphores to ensure that USB resource access occurs in a thread-safe manner, preventing concurrent access to freed memory locations. Additionally, runtime protections such as kernel address space layout randomization and stack canaries can help mitigate exploitation attempts. Organizations should also conduct regular vulnerability assessments focusing on USB subsystems and implement security monitoring to detect anomalous USB activity patterns that might indicate exploitation attempts. Given the nature of the vulnerability, it is essential to ensure that all firmware and kernel updates are applied promptly to prevent exploitation through this persistent memory corruption flaw.