CVE-2016-9191 in Linux
Summary
by MITRE
The cgroup offline implementation in the Linux kernel through 4.8.11 mishandles certain drain operations, which allows local users to cause a denial of service (system hang) by leveraging access to a container environment for executing a crafted application, as demonstrated by trinity.
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Analysis
by VulDB Data Team • 10/04/2022
The vulnerability identified as CVE-2016-9191 resides within the Linux kernel's control group cgroup subsystem, specifically affecting versions through 4.8.11. This flaw manifests in the offline implementation's handling of drain operations, creating a critical weakness that can be exploited by local attackers with container access privileges. The issue demonstrates how kernel-level subsystems can introduce severe stability risks when processing certain operational sequences, particularly within virtualized environments where containerization is prevalent.
The technical flaw occurs during the cgroup offline operation when the kernel attempts to drain resources from a control group that is being removed or deactivated. The implementation fails to properly handle certain edge cases during this drain process, leading to a deadlock condition that results in system hang. This vulnerability specifically affects the kernel's memory management and resource cleanup routines within the cgroup framework, where the drain operation becomes stuck in an infinite loop or waits indefinitely for resources that will never become available. The flaw is particularly dangerous because it can be triggered through legitimate container operations, making it difficult to distinguish from normal system behavior.
The operational impact of CVE-2016-9191 represents a significant denial of service threat that can compromise entire system stability. Local users with access to container environments can exploit this vulnerability to cause system hangs that effectively render the affected system unusable until manual intervention occurs. This vulnerability is particularly concerning in containerized environments where multiple applications share system resources and where the cgroup subsystem is actively managing resource allocation. The demonstrated exploit using the trinity test suite shows that this vulnerability can be reliably triggered through standard containerized applications, making it a serious concern for cloud providers and container orchestration platforms.
From a cybersecurity perspective, this vulnerability aligns with CWE-362, which addresses concurrent execution issues such as race conditions and deadlocks in kernel-level code. The flaw also maps to ATT&CK technique T1499.001, which covers system shutdown/reboot attacks, though in this case the impact is more subtle as a system hang rather than explicit shutdown. The vulnerability demonstrates how seemingly minor implementation details in kernel subsystems can create significant security risks, particularly when dealing with resource management and containerization technologies. Organizations running containerized workloads should prioritize patching this vulnerability as it represents a critical stability risk that can be exploited without elevated privileges, making it a prime target for both accidental and malicious exploitation.
Mitigation strategies for CVE-2016-9191 include immediate kernel updates to versions 4.8.12 or later where the vulnerability has been addressed through proper drain operation handling. System administrators should also implement monitoring solutions to detect abnormal cgroup drain operations that might indicate exploitation attempts. Container orchestration platforms should consider implementing additional resource isolation measures and regularly audit container configurations to minimize the attack surface. The fix typically involves modifying the cgroup offline implementation to properly handle drain operation completion and resource cleanup, ensuring that the kernel does not enter deadlock conditions during resource management operations. Organizations should also consider implementing security controls that limit container access to sensitive kernel operations where possible.