CVE-2020-4005: VMware ESXi Privilege Escalation Flaw

CVE-2020-4005 Overview

CVE-2020-4005 is a privilege escalation vulnerability affecting VMware ESXi hypervisor that exists in the way certain system calls are managed. A malicious actor who has already obtained privileges within the VMX process may exploit this vulnerability to escalate their privileges on the affected system. This vulnerability is particularly noteworthy because successful exploitation requires chaining with another vulnerability, such as CVE-2020-4004, making it part of a multi-stage attack chain targeting VMware virtualization infrastructure.

Critical Impact

Successful exploitation allows an attacker with VMX process access to escalate privileges on the ESXi host, potentially compromising the entire virtualization infrastructure and all hosted virtual machines.

Affected Products

• VMware ESXi 7.0 (versions before ESXi70U1b-17168206)
• VMware ESXi 6.7 (versions before ESXi670-202011101-SG)
• VMware ESXi 6.5 (versions before ESXi650-202011301-SG)
• VMware Cloud Foundation (multiple versions)

Discovery Timeline

• November 20, 2020 - CVE-2020-4005 published to NVD
• October 31, 2025 - Last updated in NVD database

Technical Details for CVE-2020-4005

Vulnerability Analysis

This vulnerability resides in the ESXi hypervisor's system call management layer. The VMX process, which is responsible for managing virtual machine execution and hardware emulation, contains a flaw in how it handles certain privileged system calls. When exploited, this flaw allows an attacker who has already compromised the VMX process to break out of its intended privilege boundary and gain elevated access on the ESXi host system.

The attack surface is limited because the attacker must first have access to the VMX process, which typically requires a prior compromise through a separate vulnerability such as CVE-2020-4004 (a use-after-free vulnerability in XHCI USB controller emulation). This chaining requirement means the vulnerability cannot be exploited in isolation but serves as a critical second stage in a more complex attack.

Root Cause

The root cause stems from improper handling of system calls within the VMX process context. The ESXi kernel does not adequately validate or restrict certain privileged operations when they originate from the VMX process, allowing a compromised VMX process to perform operations that should be restricted to higher privilege levels.

Attack Vector

The attack requires local access and follows a multi-stage exploitation path:

1. An attacker first exploits a separate vulnerability (such as CVE-2020-4004) to gain code execution within the VMX process of a virtual machine
2. From within the compromised VMX process, the attacker leverages CVE-2020-4005 to escalate privileges
3. The improper system call handling allows the attacker to escape the VMX process sandbox and gain elevated privileges on the ESXi host

This privilege escalation could allow the attacker to access other virtual machines, modify hypervisor configurations, or establish persistent access to the virtualization infrastructure.

Detection Methods for CVE-2020-4005

Indicators of Compromise

• Unexpected process behavior or privilege changes within VMX processes
• Anomalous system call patterns originating from VMX process contexts
• Unusual memory access patterns or privilege token modifications in ESXi logs
• Evidence of CVE-2020-4004 exploitation (XHCI USB controller anomalies) preceding privilege escalation attempts

Detection Strategies

• Monitor ESXi host logs for unusual VMX process activity or unexpected privilege elevations
• Implement hypervisor introspection to detect anomalous system call sequences from VMX processes
• Deploy endpoint detection on management interfaces to identify post-exploitation activity
• Correlate events between guest VMs and hypervisor for signs of VM escape attempts

Monitoring Recommendations

• Enable verbose logging on ESXi hosts to capture detailed VMX process activity
• Implement security information and event management (SIEM) rules to alert on VMX process anomalies
• Monitor for lateral movement attempts following potential hypervisor compromise
• Establish baseline VMX process behavior to identify deviations indicative of exploitation

How to Mitigate CVE-2020-4005

Immediate Actions Required

• Update VMware ESXi 7.0 to version ESXi70U1b-17168206 or later
• Update VMware ESXi 6.7 to version ESXi670-202011101-SG or later
• Update VMware ESXi 6.5 to version ESXi650-202011301-SG or later
• Review VMware Cloud Foundation deployments and apply corresponding updates
• Prioritize patching for systems where VM escape vulnerabilities like CVE-2020-4004 may also be present

Patch Information

VMware has released security patches addressing this vulnerability as part of security advisory VMSA-2020-0026. The patches modify how the ESXi kernel handles system calls from VMX processes, implementing proper privilege validation to prevent unauthorized escalation. Organizations should apply the appropriate patches based on their ESXi version:

• ESXi 7.0: Update to ESXi70U1b-17168206
• ESXi 6.7: Apply patch ESXi670-202011101-SG
• ESXi 6.5: Apply patch ESXi650-202011301-SG

Workarounds

• Limit VM access to USB passthrough functionality to reduce exposure to the chained CVE-2020-4004 vulnerability
• Restrict administrative access to ESXi hosts and vCenter management interfaces
• Implement network segmentation to isolate virtualization management traffic
• Disable unnecessary VM hardware features that could serve as initial attack vectors

# Verify ESXi patch level
esxcli system version get

# Check installed VIBs for security patches
esxcli software vib list | grep -i security

# Review USB controller configuration on VMs
vim-cmd vmsvc/getallvms | xargs -I {} vim-cmd vmsvc/device.getdevices {}