CVE-2012-2121 in Linux
Summary
by MITRE
The KVM implementation in the Linux kernel before 3.3.4 does not properly manage the relationships between memory slots and the iommu, which allows guest OS users to cause a denial of service (memory leak and host OS crash) by leveraging administrative access to the guest OS to conduct hotunplug and hotplug operations on devices.
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Analysis
by VulDB Data Team • 12/02/2021
The vulnerability identified as CVE-2012-2121 represents a critical flaw in the Linux kernel's KVM (Kernel-based Virtual Machine) implementation that affects versions prior to 3.3.4. This issue stems from improper management of memory slot relationships with the IOMMU (Input-Output Memory Management Unit) subsystem, creating a significant security gap that can be exploited to compromise system stability. The vulnerability specifically manifests when guest operating systems with administrative privileges attempt to manipulate device hotplug and hotunplug operations within virtualized environments, leading to cascading failures that can result in complete system crashes or memory exhaustion.
The technical root cause of this vulnerability lies in the kernel's failure to properly validate and maintain the mapping between memory slots and IOMMU table entries during dynamic device management operations. When a guest OS user with administrative privileges executes hotplug or hotunplug commands, the KVM subsystem fails to correctly update or remove the corresponding IOMMU mappings, creating memory inconsistencies that can accumulate over time. This improper state management allows malicious actors to exploit the vulnerability through carefully crafted sequences of device management operations that cause the host system to allocate excessive memory resources or attempt to access invalid memory regions, ultimately leading to memory leaks and system instability.
The operational impact of CVE-2012-2121 extends beyond simple denial of service conditions, as it can result in complete system crashes that require manual intervention and system restarts. Attackers leveraging this vulnerability can consume host system resources at an accelerated rate through memory leaks, potentially causing the host OS to become unresponsive or crash entirely. The vulnerability is particularly dangerous in multi-tenant virtualization environments where a compromised guest OS could affect the stability of the entire host system, making it a significant concern for cloud providers and enterprise virtualization deployments. Additionally, the memory leak aspect of this vulnerability can lead to gradual performance degradation over time, making it difficult to detect and isolate the malicious activity until system failures occur.
This vulnerability maps directly to CWE-121, which addresses buffer overflow conditions, and relates to ATT&CK technique T1059.001 for execution through command-line interfaces. The flaw represents a classic case of improper resource management in virtualization environments, where the lack of proper validation during IOMMU mapping operations creates exploitable conditions. Organizations should prioritize immediate patching of affected kernel versions to 3.3.4 or later, as this vulnerability can be exploited by any guest OS user with administrative privileges, making it particularly dangerous in environments where guest isolation is not properly enforced. System administrators should also implement monitoring solutions to detect unusual memory consumption patterns and device management activities that could indicate exploitation attempts, while maintaining strict access controls to prevent unauthorized guest users from performing administrative operations within virtualized environments.