CVE-2012-4461 in Linux
Summary
by MITRE
The KVM subsystem in the Linux kernel before 3.6.9, when running on hosts that use qemu userspace without XSAVE, allows local users to cause a denial of service (kernel OOPS) by using the KVM_SET_SREGS ioctl to set the X86_CR4_OSXSAVE bit in the guest cr4 register, then calling the KVM_RUN ioctl.
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Analysis
by VulDB Data Team • 04/19/2021
The vulnerability described in CVE-2012-4461 represents a critical flaw in the Linux kernel's KVM (Kernel-based Virtual Machine) subsystem that affects versions prior to 3.6.9. This issue specifically targets systems running virtualized environments where qemu userspace is utilized without XSAVE support, creating a scenario where local attackers can exploit kernel memory management through improper handling of virtual machine control structures. The vulnerability demonstrates a fundamental design flaw in how the kernel processes certain virtual machine register states, particularly when transitioning between different CPU feature sets during virtual machine execution.
The technical exploitation mechanism involves a specific sequence of ioctl operations that manipulate the guest's control register 4 (cr4) register through the KVM_SET_SREGS interface. When attackers set the X86_CR4_OSXSAVE bit within this register, they effectively signal to the kernel that the guest virtual machine should utilize extended save/restore functionality for processor state information. However, the kernel's implementation fails to properly validate whether the host system supports this extended feature set before allowing the operation to proceed. This mismatch between guest expectations and host capabilities results in an unhandled exception during kernel execution, manifesting as a kernel OOPS condition that terminates the virtualization subsystem.
The operational impact of this vulnerability extends beyond simple denial of service, as it represents a potential vector for more sophisticated attacks within virtualized environments. When the kernel OOPS occurs, it typically results in system instability and can potentially be leveraged to disrupt critical virtualized services running on the affected host. The vulnerability affects the integrity of the virtualization layer itself, which can have cascading effects on multiple virtual machines sharing the same host system. From a cybersecurity perspective, this represents a privilege escalation vector that could be exploited by malicious actors with local access to gain control over the virtualization infrastructure.
Mitigation strategies for this vulnerability require immediate kernel updates to versions 3.6.9 or later, where the proper validation checks have been implemented to prevent the unsafe manipulation of control registers. System administrators should also implement monitoring solutions to detect unusual patterns of ioctl operations that might indicate exploitation attempts. The vulnerability aligns with CWE-121, which addresses buffer overflow conditions, and can be mapped to ATT&CK technique T1059.001 for execution through kernel-level exploits. Organizations should conduct thorough vulnerability assessments of their virtualization environments and ensure that all virtualization hosts are running patched kernel versions to prevent exploitation of this and similar vulnerabilities in the KVM subsystem.