CVE-2012-1179 in Linux
Summary
by MITRE
The Linux kernel before 3.3.1, when KVM is used, allows guest OS users to cause a denial of service (host OS crash) by leveraging administrative access to the guest OS, related to the pmd_none_or_clear_bad function and page faults for huge pages.
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Analysis
by VulDB Data Team • 03/22/2021
The vulnerability identified as CVE-2012-1179 represents a critical denial of service flaw affecting Linux kernel versions prior to 3.3.1 when utilizing Kernel-based Virtual Machine KVM virtualization technology. This vulnerability specifically targets the interaction between guest operating systems and host systems through the pmd_none_or_clear_bad function, which handles page fault management for huge pages within virtualized environments. The flaw enables malicious guest users with administrative privileges to craft specific page fault conditions that can trigger kernel panics and subsequent host system crashes, effectively compromising the stability and availability of virtualized infrastructure.
The technical implementation of this vulnerability stems from improper handling of page table entries during huge page fault processing within the KVM subsystem. When a guest operating system attempts to access memory regions that trigger page faults for huge pages, the pmd_none_or_clear_bad function fails to properly validate or handle the page table entry states. This function is responsible for checking whether a page table entry is either empty or contains invalid entries, but the implementation contains a logic flaw that allows crafted page fault conditions to bypass proper validation mechanisms. The vulnerability specifically manifests when the kernel attempts to clear bad page table entries without adequate state verification, leading to memory corruption and kernel panic conditions that result in complete host system crashes.
From an operational perspective, this vulnerability poses significant risks to virtualized environments where guest operating systems may be compromised or controlled by malicious actors with administrative privileges. The impact extends beyond simple denial of service as it can lead to complete system outages affecting multiple virtual machines running on the same host. The vulnerability requires guest users to have administrative access, which means that even in well-secured environments, privileged guest users could potentially exploit this flaw. Organizations running KVM-based virtualization platforms with affected kernel versions face substantial operational risks, including service disruption, data loss, and potential compromise of the entire virtualized infrastructure. The vulnerability also demonstrates the complexity of virtualization security where guest-level privileges can translate into host-level system compromise.
The underlying weakness aligns with CWE-119 Improper Access to Memory and CWE-248 Uncaught Exception, specifically manifesting as an improper handling of memory page states during virtualization operations. This vulnerability can be mapped to ATT&CK technique T1499.004 Network Denial of Service within the context of virtualized environments, where adversaries leverage system vulnerabilities to disrupt services. The attack vector requires a guest user with administrative privileges, making it particularly concerning in multi-tenant virtualization environments where different users may have varying privilege levels. Mitigation strategies should focus on immediate kernel upgrades to version 3.3.1 or later, which contain the necessary fixes to properly validate page table entries and prevent the exploitation of this memory handling flaw. Organizations should also implement monitoring for unusual page fault patterns and consider additional virtualization security measures such as memory isolation and privilege separation to minimize the attack surface.
This vulnerability highlights the critical importance of proper memory management in virtualized environments and demonstrates how seemingly isolated guest operating systems can impact host system stability. The flaw represents a classic example of how virtualization security boundaries can be crossed through improper kernel implementation, emphasizing the need for comprehensive security testing of virtualization components. The vulnerability's impact extends beyond immediate system crashes to include potential data integrity issues and service availability concerns in enterprise environments relying heavily on virtualized infrastructure. Organizations should conduct thorough vulnerability assessments of their virtualization environments and ensure timely patch deployment to protect against similar memory management flaws that could potentially be exploited for more sophisticated attacks.