CVE-2011-4622 in Linux
Summary
by MITRE
The create_pit_timer function in arch/x86/kvm/i8254.c in KVM 83, and possibly other versions, does not properly handle when Programmable Interval Timer (PIT) interrupt requests (IRQs) when a virtual interrupt controller (irqchip) is not available, which allows local users to cause a denial of service (NULL pointer dereference) by starting a timer.
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Analysis
by VulDB Data Team • 03/20/2021
The vulnerability identified as CVE-2011-4622 resides within the Kernel-based Virtual Machine (KVM) subsystem of the Linux kernel, specifically in the i8254.c file that manages the Programmable Interval Timer functionality. This issue affects KVM version 83 and potentially other versions, representing a critical flaw in virtualization infrastructure that could be exploited by local attackers to disrupt system operations. The vulnerability stems from improper handling of interrupt request processing within the virtual machine environment, creating a scenario where a null pointer dereference can occur under specific conditions.
The technical flaw manifests in the create_pit_timer function which fails to adequately validate the presence of a virtual interrupt controller before attempting to process PIT interrupt requests. When a virtual machine attempts to start a timer without an available irqchip, the function proceeds with operations that ultimately lead to accessing a null pointer reference. This condition occurs because the code path does not properly check whether the interrupt controller structure has been initialized or is available before attempting to use it. The vulnerability is particularly concerning as it operates at the kernel level within the virtualization layer, making it accessible to any local user who can execute code within the virtual environment.
The operational impact of this vulnerability extends beyond simple denial of service, as it represents a fundamental flaw in how KVM handles timer initialization in virtualized environments. Local attackers can exploit this weakness to crash the virtual machine or even the entire host system, depending on the execution context and system configuration. The null pointer dereference results in an immediate system crash or kernel panic, effectively rendering the virtual machine unusable and potentially causing broader system instability. This type of vulnerability directly impacts the reliability and security posture of virtualized environments where KVM is deployed, particularly in cloud computing and server virtualization scenarios where multiple virtual machines share the same physical host.
Mitigation strategies for CVE-2011-4622 should focus on both immediate patching and architectural considerations. The primary solution involves applying the official kernel patches that address the null pointer dereference in the create_pit_timer function by implementing proper validation checks before accessing interrupt controller structures. Organizations should also consider implementing additional monitoring and alerting mechanisms to detect potential exploitation attempts, as the vulnerability can be triggered through legitimate timer operations within virtual machines. From a security perspective, this vulnerability aligns with CWE-476 which describes NULL pointer dereference conditions, and represents a classic example of insufficient input validation in kernel space code. The ATT&CK framework would categorize this as a privilege escalation technique through kernel exploitation, as local users can leverage this flaw to gain control over system resources and potentially escalate their privileges within the virtualized environment.