CVE-2012-1601 in Linux
Summary
by MITRE
The KVM implementation in the Linux kernel before 3.3.6 allows host OS users to cause a denial of service (NULL pointer dereference and host OS crash) by making a KVM_CREATE_IRQCHIP ioctl call after a virtual CPU already exists.
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Analysis
by VulDB Data Team • 03/24/2021
The vulnerability described in CVE-2012-1601 represents a critical flaw in the Kernel-based Virtual Machine (KVM) implementation within the Linux kernel version 3.3.5 and earlier. This issue arises from improper handling of ioctl system calls within the virtualization subsystem, specifically affecting the KVM_CREATE_IRQCHIP functionality. The vulnerability exists in the kernel's virtualization framework where the KVM module fails to properly validate the sequence of operations when creating interrupt controller chips for virtual machines. The flaw occurs when a host operating system user attempts to execute the KVM_CREATE_IRQCHIP ioctl call after a virtual CPU instance has already been initialized within the same virtual machine context. This particular sequence of operations creates a dangerous condition that leads to a NULL pointer dereference, ultimately resulting in a system crash of the host operating system.
The technical nature of this vulnerability stems from a lack of proper state validation within the KVM subsystem's ioctl handling mechanism. When the KVM_CREATE_IRQCHIP ioctl is invoked, the kernel code does not adequately check whether the virtual machine configuration is in a valid state for creating additional interrupt controller components. This oversight creates a race condition scenario where the system attempts to access memory locations that have not been properly initialized or allocated. The vulnerability is classified under CWE-476 as a NULL pointer dereference, which represents a fundamental programming error where code attempts to access memory through a pointer that has not been properly initialized. The improper validation of virtual machine state transitions allows malicious or malformed ioctl calls to bypass normal execution paths and trigger kernel memory corruption.
From an operational perspective, this vulnerability presents a significant threat to virtualized environments where host systems are running vulnerable kernel versions. An attacker with access to the host operating system or the ability to execute code within a guest virtual machine could potentially exploit this weakness to cause a complete system crash of the host. The denial of service impact extends beyond simple system unavailability as it can lead to complete loss of virtualization services, potentially affecting multiple virtual machines running on the same host system. The vulnerability is particularly concerning in cloud computing environments where multiple tenants share the same physical infrastructure, as a successful exploitation could result in service disruption for all virtual machines hosted on the compromised system. The attack vector requires minimal privileges since it can be triggered by host OS users, making it an attractive target for both malicious actors and system administrators seeking to disrupt services.
The mitigation strategies for CVE-2012-1601 primarily involve upgrading the Linux kernel to version 3.3.6 or later, where the vulnerability has been addressed through proper state validation and error handling mechanisms. System administrators should also implement strict access controls on virtualization interfaces and monitor for unusual ioctl call patterns that might indicate attempted exploitation. The fix implemented in kernel version 3.3.6 includes enhanced validation of virtual machine state transitions and proper handling of the KVM_CREATE_IRQCHIP ioctl call sequence. Additionally, organizations should consider implementing virtualization-specific security measures such as hypervisor hardening, regular security audits of virtualization components, and maintaining up-to-date virtualization management software. This vulnerability aligns with ATT&CK technique T1059.003 for executing malicious code within virtualized environments and represents a classic example of how virtualization security flaws can be leveraged to compromise host system integrity, making it a critical concern for enterprise security teams managing virtualized infrastructures.