CVE-2017-12168 in Linux
Summary
by MITRE
The access_pmu_evcntr function in arch/arm64/kvm/sys_regs.c in the Linux kernel before 4.8.11 allows privileged KVM guest OS users to cause a denial of service (assertion failure and host OS crash) by accessing the Performance Monitors Cycle Count Register (PMCCNTR).
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Analysis
by VulDB Data Team • 12/29/2022
The vulnerability described in CVE-2017-12168 represents a critical flaw in the Linux kernel's virtualization subsystem that affects systems utilizing ARM64 architecture with KVM hypervisor capabilities. This issue resides within the access_pmu_evcntr function located in arch/arm64/kvm/sys_regs.c, specifically targeting the Performance Monitors Cycle Count Register (PMCCNTR) which is part of the ARM Performance Monitoring Unit implementation. The flaw manifests when privileged guest operating systems attempt to access this particular register, creating a condition that can be exploited to trigger system instability and complete system crashes.
The technical nature of this vulnerability stems from improper validation and handling of access requests to the PMCCNTR register within the KVM hypervisor's system register interface. When a privileged guest OS user attempts to read or write to this specific register, the kernel fails to properly validate the access parameters, leading to an assertion failure that ultimately results in a kernel panic and host system crash. This represents a classic case of inadequate input validation and error handling within kernel space code, where the absence of proper bounds checking and access control mechanisms allows malicious or malformed register access to propagate to critical system components. The vulnerability falls under CWE-248, which specifically addresses "Uncaught Exception" conditions in software systems.
The operational impact of this vulnerability extends beyond simple denial of service, as it can be exploited to cause complete system instability and potential data loss in virtualized environments. In enterprise settings where KVM-based virtualization is prevalent, particularly in cloud computing and server consolidation scenarios, this vulnerability poses significant risks to system availability and reliability. Attackers with access to privileged guest operating systems can leverage this flaw to repeatedly crash the host system, effectively rendering virtualized services unavailable and potentially causing cascading failures across dependent systems. The vulnerability is particularly concerning because it allows for remote exploitation within the guest environment, meaning that a compromised guest could be used to attack the host system without requiring direct access to the host itself.
Mitigation strategies for CVE-2017-12168 should prioritize immediate kernel updates to versions 4.8.11 or later, which contain the necessary patches addressing the assertion failure in the access_pmu_evcntr function. Organizations should also implement monitoring solutions to detect unusual patterns of register access that might indicate exploitation attempts, and consider implementing additional isolation measures between guest operating systems to limit the potential impact of successful attacks. The fix implemented in the patched kernel versions addresses the root cause by properly validating register access requests and implementing appropriate error handling mechanisms that prevent the assertion failure from propagating to the host system. This vulnerability demonstrates the importance of thorough testing and validation of virtualization interfaces, particularly those that provide direct access to hardware performance monitoring features, as outlined in the ATT&CK framework's techniques for privilege escalation and defense evasion through system-level exploitation.