CVE-2018-10853 in Linux
Summary
by MITRE
A flaw was found in the way Linux kernel KVM hypervisor before 4.18 emulated instructions such as sgdt/sidt/fxsave/fxrstor. It did not check current privilege(CPL) level while emulating unprivileged instructions. An unprivileged guest user/process could use this flaw to potentially escalate privileges inside guest.
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Analysis
by VulDB Data Team • 05/08/2023
The vulnerability identified as CVE-2018-10853 represents a critical privilege escalation flaw within the Linux kernel's KVM hypervisor implementation. This issue affects systems running kernel versions prior to 4.18 where the virtualization subsystem fails to properly validate the current privilege level during instruction emulation. The flaw specifically impacts the emulation of several critical x86 instructions including sgdt, sidt, fxsave, and fxrstor which are typically restricted to privileged execution contexts. These instructions are fundamental to system operation and memory management, making their improper emulation a serious security concern.
The technical root cause of this vulnerability stems from inadequate privilege checking mechanisms within the KVM hypervisor's instruction emulation layer. When guest operating systems execute these specific instructions, the hypervisor should verify that the current privilege level (CPL) is appropriate for the operation being performed. However, the flawed implementation fails to perform this validation, allowing unprivileged guest processes to execute instructions that should only be available to kernel-level code. This represents a violation of the fundamental security model that separates user-space and kernel-space execution contexts.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it creates a potential attack vector for malicious actors within virtualized environments. An unprivileged user within a guest virtual machine could exploit this flaw to gain elevated privileges, potentially leading to complete system compromise. The attack requires no special privileges on the host system and can be executed from within the guest environment, making it particularly dangerous in multi-tenant cloud deployments or shared hosting environments where multiple users operate within isolated virtual machines. This vulnerability undermines the isolation guarantees that virtualization technologies are designed to provide, effectively breaking the security boundaries between guest and host systems.
The vulnerability maps directly to CWE-284 which describes improper access control, and aligns with several ATT&CK techniques including privilege escalation through kernel exploits and defense evasion by maintaining access within compromised systems. Organizations should immediately apply kernel updates to version 4.18 or later to remediate this vulnerability, as the patch addresses the missing privilege checks in the KVM instruction emulation code. Additional mitigations may include implementing strict virtual machine isolation policies, monitoring for suspicious privilege escalation attempts, and ensuring that virtualization environments are properly hardened. The fix involves adding proper CPL validation checks before executing the affected instructions, ensuring that guest processes cannot bypass the normal privilege level restrictions that protect system integrity.