CVE-2020-3981 in ESXi
Summary
by MITRE • 10/21/2020
VMware ESXi (7.0 before ESXi_7.0.1-0.0.16850804, 6.7 before ESXi670-202008101-SG, 6.5 before ESXi650-202007101-SG), Workstation (15.x), Fusion (11.x before 11.5.6) contain an out-of-bounds read vulnerability due to a time-of-check time-of-use issue in ACPI device. A malicious actor with administrative access to a virtual machine may be able to exploit this issue to leak memory from the vmx process.
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Analysis
by VulDB Data Team • 11/22/2020
The vulnerability identified as CVE-2020-3981 represents a critical out-of-bounds read flaw affecting multiple VMware virtualization products including ESXi hypervisor versions, Workstation, and Fusion desktop virtualization solutions. This vulnerability stems from a time-of-check time-of-use issue within the ACPI device implementation, creating a window where system state can be manipulated between validation and execution phases. The flaw specifically impacts systems running VMware ESXi versions prior to ESXi_7.0.1-0.0.16850804, ESXi670-202008101-SG, and ESXi650-202007101-SG, alongside VMware Workstation 15.x and Fusion 11.x versions before 11.5.6. The root cause lies in improper handling of ACPI device operations where the system performs validation checks before executing operations, but the underlying state can change during this interval, leading to memory access violations.
The technical exploitation of this vulnerability requires an attacker to possess administrative privileges within a guest virtual machine, which significantly reduces the attack surface but does not eliminate the risk entirely. When a malicious actor leverages this flaw, they can trigger memory leakage from the vmx process, which is the core virtual machine monitor process responsible for managing guest operating systems. This memory disclosure can potentially expose sensitive information including cryptographic keys, user credentials, or system configuration data that resides in memory. The vulnerability operates at the hypervisor level, making it particularly dangerous as it can potentially be used to escalate privileges or extract confidential information that would normally be isolated within virtual machine boundaries. According to CWE classification, this vulnerability maps to CWE-125: Out-of-bounds Read, which is a fundamental memory safety issue that occurs when a program attempts to read data from memory locations outside the bounds of a buffer. The attack pattern aligns with ATT&CK technique T1059.001: Command and Scripting Interpreter - PowerShell, as exploitation may involve crafting specific ACPI commands that trigger the memory access violation.
The operational impact of this vulnerability extends beyond simple information disclosure, as it creates potential pathways for more sophisticated attacks within virtualized environments. The memory leakage could provide attackers with enough information to perform further exploitation attempts, including heap spraying, return-oriented programming, or other advanced techniques that rely on knowing memory layout details. Organizations running affected VMware products face significant risk as this vulnerability could enable attackers to compromise virtual machine isolation, potentially allowing lateral movement between VMs or access to data that should remain protected within individual virtual environments. The vulnerability's presence in both server and desktop virtualization products means that organizations with hybrid deployments may face increased attack surface complexity. The timing of the vulnerability disclosure coincides with a period of heightened cybersecurity attention around virtualization platforms, making it particularly concerning for enterprises that rely heavily on VMware infrastructure for their computing environments.
Mitigation strategies for CVE-2020-3981 focus primarily on applying official patches provided by VMware, which address the underlying time-of-check time-of-use issue in ACPI device handling. Organizations should prioritize updating all affected VMware products to their patched versions, with particular attention to ESXi hypervisor installations which represent the most critical deployment scenario. System administrators should implement network segmentation and access controls to limit administrative privileges within guest operating systems, as the vulnerability requires elevated access to exploit. Additionally, monitoring for unusual memory access patterns or unexpected vmx process behavior can help detect potential exploitation attempts. The patching process should be carefully planned to minimize service disruption while ensuring all vulnerable systems receive protection. Organizations should also conduct vulnerability assessments to identify all affected systems and prioritize remediation based on risk exposure. Regular security audits of virtualization environments can help identify additional vulnerabilities that may exist alongside this one, particularly focusing on input validation and memory management practices within hypervisor components. The vulnerability highlights the importance of maintaining up-to-date virtualization infrastructure and demonstrates the critical need for comprehensive security testing of hypervisor components that handle device interaction and resource management.