CVE-2009-1242 in Linux
Summary
by MITRE
The vmx_set_msr function in arch/x86/kvm/vmx.c in the VMX implementation in the KVM subsystem in the Linux kernel before 2.6.29.1 on the i386 platform allows guest OS users to cause a denial of service (OOPS) by setting the EFER_LME (aka "Long mode enable") bit in the Extended Feature Enable Register (EFER) model-specific register, which is specific to the x86_64 platform.
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Analysis
by VulDB Data Team • 05/23/2025
The vulnerability described in CVE-2009-1242 represents a critical design flaw in the Linux kernel's KVM virtualization subsystem, specifically within the VMX implementation on i386 platforms. This issue affects kernel versions prior to 2.6.29.1 and demonstrates a fundamental misunderstanding of platform-specific register handling within virtualized environments. The vulnerability occurs in the vmx_set_msr function which is responsible for managing model-specific registers in Intel's Virtual Machine Extensions technology. When a guest operating system attempts to manipulate the Extended Feature Enable Register (EFER) by setting the EFER_LME bit, the kernel fails to properly validate the platform compatibility of this operation, leading to a kernel oops condition that results in system instability.
The technical root cause of this vulnerability stems from the improper handling of x86_64 specific features on i386 platforms within the KVM subsystem. The EFER_LME bit, which enables long mode execution on x86_64 processors, should not be available or properly handled on 32-bit i386 systems where long mode is not supported. The vmx_set_msr function lacks proper validation to ensure that operations targeting x86_64 specific registers are only permitted when running on appropriate hardware platforms. This oversight creates a scenario where guest operating systems can inadvertently trigger kernel panics by attempting to enable features that are not supported on the underlying architecture, resulting in a denial of service condition that can crash the entire virtualization host.
The operational impact of this vulnerability extends beyond simple system instability, as it represents a potential vector for attackers to disrupt virtualized environments and compromise the availability of critical services. When a guest OS user successfully triggers this vulnerability, the kernel experiences an unhandled exception that manifests as an OOPS message, effectively terminating the virtual machine's operation and potentially causing cascading failures in larger virtualized infrastructures. This type of vulnerability directly relates to CWE-122, which describes buffer overflow conditions that can lead to denial of service, and aligns with ATT&CK technique T1499.004 for network denial of service. The vulnerability is particularly concerning in cloud computing environments where multiple virtual machines share the same physical host, as a single compromised guest could potentially affect the availability of all other virtual machines running on that host.
Mitigation strategies for this vulnerability require immediate kernel updates to versions 2.6.29.1 or later where the proper platform validation has been implemented. System administrators should prioritize patching affected systems and ensure that all virtualization hosts are running patched kernel versions. Additionally, monitoring for kernel oops messages and system stability issues can help detect potential exploitation attempts. The fix implemented in the patched kernel versions involves adding proper validation checks within the vmx_set_msr function to prevent setting x86_64 specific bits on i386 platforms, ensuring that only appropriate register modifications are allowed based on the underlying hardware capabilities. This vulnerability underscores the importance of proper virtualization layer validation and demonstrates how platform-specific feature handling can create unexpected security implications in complex virtualized environments.