CVE-2016-6786 in Linux
Summary
by MITRE
kernel/events/core.c in the performance subsystem in the Linux kernel before 4.0 mismanages locks during certain migrations, which allows local users to gain privileges via a crafted application, aka Android internal bug 30955111.
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Analysis
by VulDB Data Team • 10/12/2022
The vulnerability identified as CVE-2016-6786 resides within the Linux kernel's performance subsystem, specifically in the kernel/events/core.c file. This flaw represents a critical privilege escalation vulnerability that affects Linux kernel versions prior to 4.0. The issue manifests during specific migration operations within the performance monitoring framework, where improper lock management creates exploitable conditions that malicious local users can leverage to elevate their privileges. The vulnerability was particularly significant as it was also identified as Android internal bug 30955111, indicating its impact extends to mobile device security where Linux kernel components are utilized.
The technical root cause of this vulnerability stems from improper lock handling during thread migration operations within the performance subsystem. When the kernel attempts to migrate performance monitoring events between different threads or processors, the locking mechanism fails to properly synchronize access to shared resources. This race condition occurs in the performance monitoring core functionality where locks are not correctly acquired or released during migration scenarios, creating opportunities for malicious code to manipulate the system state. The flaw specifically involves the interaction between different locking primitives and the migration code paths that handle performance event tracking, allowing attackers to exploit timing windows where locks are temporarily unavailable or improperly managed.
The operational impact of CVE-2016-6786 is severe as it enables local privilege escalation from user-level processes to kernel-level privileges. An attacker with local access to a system can craft a malicious application that triggers the specific migration scenario where locks are mismanaged, ultimately gaining root access to the system. This vulnerability is particularly dangerous in multi-user environments or systems where users may have limited privileges but could exploit this flaw to gain complete system control. The privilege escalation occurs because the performance subsystem operates with elevated privileges, and the improper lock management allows attackers to manipulate kernel data structures that control access permissions and system resources. This vulnerability aligns with CWE-362, which describes a race condition in lock management, and represents a classic example of how kernel-level concurrency issues can lead to critical security breaches.
Mitigation strategies for CVE-2016-6786 primarily involve upgrading to Linux kernel version 4.0 or later, where the lock management issues have been resolved through proper synchronization mechanisms. System administrators should prioritize patching affected systems, particularly those running kernel versions between 2.6.32 and 3.19, which are most vulnerable to this exploit. Additionally, implementing runtime protections such as kernel address space layout randomization and enabling security modules like SELinux or AppArmor can provide additional layers of defense against exploitation attempts. The fix implemented in kernel 4.0 addresses the underlying race condition by ensuring proper lock acquisition and release during migration operations, preventing the exploitation scenario that led to privilege escalation. Organizations should also monitor for similar vulnerabilities in other kernel subsystems and maintain comprehensive patch management processes to protect against future exploits that may leverage similar concurrency issues. This vulnerability demonstrates the importance of proper locking mechanisms in kernel code and aligns with ATT&CK technique T1068, which covers privilege escalation through local exploitation of kernel vulnerabilities.