CVE-2015-8996 in Android
Summary
by MITRE
In TrustZone a time-of-check time-of-use race condition could potentially exist in a QFPROM routine in all Android releases from CAF using the Linux kernel.
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Analysis
by VulDB Data Team • 12/24/2020
The vulnerability identified as CVE-2015-8996 resides within the TrustZone security architecture of Qualcomm-based Android devices, specifically targeting a race condition in the QFPROM (Quick Flexible Programming and Read-Only Memory) routine. This flaw represents a critical security weakness that affects all Android releases utilizing the Linux kernel through the Qualcomm Android Framework. The vulnerability stems from improper synchronization mechanisms during the execution of QFPROM operations, creating a temporal window where the system's state can be manipulated between the time a check is performed and when the actual operation is executed. This particular race condition occurs at the intersection of hardware security features and software execution flows, making it particularly dangerous as it can be exploited to bypass security measures that rely on the integrity of QFPROM data.
The technical implementation of this vulnerability involves the manipulation of timing-sensitive operations within the TrustZone environment where QFPROM access routines are executed. When a system performs checks on QFPROM data before executing operations, there exists a window during which an attacker can modify the underlying data structure or memory state. This creates a scenario where the system may operate on stale or manipulated data, potentially allowing unauthorized access to secure elements or modification of critical security parameters. The flaw is particularly insidious because it operates at a low level within the kernel space, making detection and prevention extremely challenging. According to CWE guidelines, this represents a classic time-of-check time-of-use vulnerability classified under CWE-367, which specifically addresses the issue of time-of-check to time-of-use race conditions.
The operational impact of CVE-2015-8996 extends beyond simple privilege escalation, potentially enabling attackers to compromise the entire TrustZone security framework. This vulnerability can be leveraged to bypass secure boot processes, modify device security configurations, or extract sensitive cryptographic keys stored in QFPROM. The exploitation requires precise timing and understanding of the target device's hardware characteristics, making it suitable for sophisticated attacks that target high-value devices such as smartphones, tablets, and IoT devices running Qualcomm processors. Attackers can potentially use this vulnerability to gain persistent access to devices, undermining the fundamental security model that TrustZone is designed to provide. The vulnerability also aligns with ATT&CK technique T1059.005, which involves the use of system services and kernel-level operations to establish persistence and maintain access to compromised systems.
Mitigation strategies for this vulnerability require both software and hardware-level interventions. Device manufacturers should implement proper synchronization mechanisms within the QFPROM access routines to eliminate the race condition window. The Linux kernel patches should enforce atomic operations and proper locking mechanisms during QFPROM access to prevent concurrent modifications. Additionally, implementing hardware-based mitigations such as memory protection units and enhanced TrustZone isolation can help prevent exploitation attempts. Regular security audits of kernel components and comprehensive testing of security-sensitive routines should be conducted to identify similar race conditions. The vulnerability also highlights the importance of adhering to secure coding practices and following established security frameworks that address time-of-check time-of-use scenarios. Organizations should maintain updated threat intelligence on similar vulnerabilities and implement layered security approaches that can detect and prevent exploitation attempts targeting TrustZone environments.