CVE-2014-8481 in Linux
Summary
by MITRE
The instruction decoder in arch/x86/kvm/emulate.c in the KVM subsystem in the Linux kernel before 3.18-rc2 does not properly handle invalid instructions, which allows guest OS users to cause a denial of service (NULL pointer dereference and host OS crash) via a crafted application that triggers (1) an improperly fetched instruction or (2) an instruction that occupies too many bytes. NOTE: this vulnerability exists because of an incomplete fix for CVE-2014-8480.
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Analysis
by VulDB Data Team • 02/23/2022
The vulnerability described in CVE-2014-8481 represents a critical flaw in the Linux kernel's KVM (Kernel-based Virtual Machine) subsystem that affects virtualization environments. This issue resides in the instruction decoder component located at arch/x86/kvm/emulate.c, which is responsible for emulating x86 instructions within virtual machine environments. The vulnerability specifically targets the handling of invalid instructions within the kernel's virtualization framework, creating a pathway for malicious guest operating systems to disrupt host system operations. The flaw manifests when the kernel fails to properly validate instruction fetch operations or handle instructions that exceed normal byte limits, leading to system instability and potential complete system crashes.
The technical implementation of this vulnerability stems from an incomplete remediation of a previous vulnerability, CVE-2014-8480, which indicates that developers attempted to address similar issues but failed to fully resolve the underlying problem. When a malicious guest OS executes a crafted application that triggers either an improperly fetched instruction or an instruction that occupies an excessive number of bytes, the kernel's instruction decoder encounters a NULL pointer dereference condition. This occurs because the decoder does not adequately validate input parameters before attempting to process instruction data, particularly when dealing with malformed or oversized instruction sequences that could originate from malicious code within a virtualized environment.
The operational impact of CVE-2014-8481 extends beyond simple denial of service to potentially catastrophic system failures that can compromise entire virtualization infrastructures. Host operating systems running vulnerable kernel versions become susceptible to crashes that can affect multiple virtual machines simultaneously, as the NULL pointer dereference propagates through the kernel's memory management subsystem. This vulnerability particularly threatens cloud computing environments, virtualized data centers, and any infrastructure relying on KVM-based virtualization where guest OS users might have elevated privileges or access to execute malicious code. The vulnerability's severity is compounded by the fact that it can be exploited by unprivileged guest users, making it particularly dangerous in multi-tenant environments where isolation between virtual machines is expected.
Security practitioners should implement immediate mitigations including kernel version updates to 3.18-rc2 or later, which contain the complete fix for both CVE-2014-8480 and CVE-2014-8481. Organizations should also consider implementing additional monitoring and logging around virtualization subsystems to detect anomalous instruction execution patterns that might indicate exploitation attempts. The vulnerability aligns with ATT&CK technique T1059.005 for command and scripting interpreter, as it allows for execution of malicious code within virtualized environments. From a CWE perspective, this vulnerability maps to CWE-476 NULL Pointer Dereference, representing a classic software security flaw where improper input validation leads to system crashes. Organizations should also review their virtualization security policies and consider implementing microsegmentation or additional isolation measures to limit potential impact from compromised guest environments. The vulnerability demonstrates the critical importance of complete patch management and thorough regression testing when addressing security vulnerabilities in complex kernel subsystems.