CVE-2014-3690 in Linux
Summary
by MITRE
arch/x86/kvm/vmx.c in the KVM subsystem in the Linux kernel before 3.17.2 on Intel processors does not ensure that the value in the CR4 control register remains the same after a VM entry, which allows host OS users to kill arbitrary processes or cause a denial of service (system disruption) by leveraging /dev/kvm access, as demonstrated by PR_SET_TSC prctl calls within a modified copy of QEMU.
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Analysis
by VulDB Data Team • 02/23/2022
The vulnerability described in CVE-2014-3690 represents a critical flaw in the Kernel-based Virtual Machine (KVM) implementation within the Linux kernel version 3.17.2 and earlier. This issue specifically affects Intel processor architectures and resides in the vmx.c file within the KVM subsystem. The vulnerability stems from insufficient validation of the CR4 control register during virtual machine entry operations, creating a potential pathway for privilege escalation and system compromise. The flaw is particularly concerning because it can be exploited by users with access to /dev/kvm, which is typically available to unprivileged users in many Linux distributions.
The technical implementation of this vulnerability exploits a weakness in the virtualization infrastructure where the CR4 register value is not properly maintained across VM entry transitions. In virtualized environments, the CR4 register controls various processor features including paging, protection, and virtualization extensions. When a virtual machine transitions from guest mode back to host mode, the system should preserve the CR4 register state to maintain system integrity. However, this vulnerability allows malicious code to manipulate the CR4 register value during VM entry, potentially enabling unauthorized access to system resources and processes.
The operational impact of this vulnerability extends beyond simple privilege escalation to include potential system disruption and arbitrary process termination. Attackers with access to the /dev/kvm device can leverage this flaw to execute malicious code that manipulates the CR4 register, potentially causing system instability or complete system crashes. The demonstration using PR_SET_TSC prctl calls within a modified QEMU instance shows how this vulnerability can be exploited in practice, where the malicious code can force the system to reset the time-stamp counter and potentially kill arbitrary processes. This capability aligns with ATT&CK technique T1068, which involves privilege escalation through the exploitation of system vulnerabilities.
The vulnerability's exploitation path demonstrates a clear security boundary violation where host OS users can manipulate system-level registers to affect system behavior. This issue is categorized under CWE-284, which addresses inadequate access control, and also relates to CWE-362, concerning concurrent execution using shared resources. The flaw essentially allows for a form of privilege escalation where unprivileged users can gain access to system resources that should be restricted to privileged processes. The potential for denial of service through system disruption makes this vulnerability particularly dangerous in production environments where virtualization is extensively used.
Mitigation strategies for CVE-2014-3690 primarily involve upgrading to Linux kernel versions 3.17.2 or later, where the vulnerability has been patched. Organizations should also implement proper access controls to limit /dev/kvm access to only trusted users and processes. System administrators should monitor for unauthorized access to virtualization interfaces and consider implementing additional security measures such as mandatory access controls or security modules that can prevent unauthorized manipulation of system registers. The patch addresses the core issue by ensuring proper validation and preservation of CR4 register values during VM entry operations, effectively closing the security gap that allowed for this type of exploitation.
This vulnerability highlights the critical importance of proper virtualization security implementation and demonstrates how flaws in hypervisor components can have far-reaching consequences for system security. The issue serves as a reminder of the need for comprehensive security testing of virtualization infrastructure and the importance of maintaining up-to-date kernel versions to protect against known vulnerabilities. Organizations utilizing KVM or similar virtualization technologies should conduct thorough security assessments of their virtualization environments and ensure proper patch management protocols are in place to protect against similar vulnerabilities.