CVE-2020-4004 in ESXi
Summary
by MITRE • 11/21/2020
VMware ESXi (7.0 before ESXi70U1b-17168206, 6.7 before ESXi670-202011101-SG, 6.5 before ESXi650-202011301-SG), Workstation (15.x before 15.5.7), Fusion (11.x before 11.5.7) contain a use-after-free vulnerability in the XHCI USB controller. A malicious actor with local administrative privileges on a virtual machine may exploit this issue to execute code as the virtual machine's VMX process running on the host.
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Analysis
by VulDB Data Team • 10/31/2025
The vulnerability identified as CVE-2020-4004 represents a critical use-after-free flaw within VMware's virtualization platforms, specifically affecting ESXi hypervisor versions and VMware Workstation and Fusion desktop products. This vulnerability resides in the XHCI USB controller implementation and fundamentally compromises the security boundary between virtual machines and their underlying host systems. The flaw manifests when a malicious actor with local administrative privileges within a guest operating system can leverage this vulnerability to escalate privileges and execute arbitrary code within the context of the VMX process on the host machine. This represents a significant escalation from standard guest-to-host privilege boundaries and demonstrates the severe implications of hypervisor-level vulnerabilities.
The technical nature of this vulnerability aligns with CWE-416, which defines use-after-free conditions as a class of memory safety issues where a program continues to reference memory after it has been freed. In the context of virtualization, this occurs within the XHCI USB controller driver implementation where improper memory management allows for a freed memory block to be accessed by subsequent operations. The XHCI (eXtensible Host Controller Interface) USB controller is responsible for managing USB device communications between virtual machines and the physical host hardware, making it a critical component in the virtualization stack. When the memory allocated for USB controller operations is freed but not properly invalidated, malicious code within a compromised guest can manipulate the memory layout to achieve code execution in the privileged host context.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it enables attackers to potentially compromise the entire host system and all virtual machines running on it. This represents a direct violation of the fundamental security principle that virtual machines should be isolated from each other and from the host system. The attack vector requires local administrative access within a guest machine, which is often achievable through social engineering, credential theft, or exploitation of other vulnerabilities in the guest environment. Once exploited, the vulnerability allows for complete compromise of the host's VMX process, which operates with elevated privileges and controls the virtualization environment. This creates a pathway for attackers to access sensitive data, monitor network traffic, or establish persistent access to the host system and all its virtualized resources.
From a threat modeling perspective, this vulnerability maps to several ATT&CK techniques including privilege escalation through use-after-free conditions and execution through legitimate system processes. The vulnerability's exploitation requires minimal network access beyond what's already available within the guest environment, making it particularly dangerous in multi-tenant cloud environments or shared infrastructure scenarios. Organizations running affected VMware products face significant risk, as this vulnerability can be exploited without requiring network-based attacks or sophisticated exploitation techniques. The remediation approach involves applying official VMware patches and updates, which address the memory management issues in the XHCI USB controller implementation. Security teams should prioritize patching affected systems and consider implementing additional monitoring for suspicious VMX process behavior or unexpected privilege escalation events. The vulnerability highlights the critical importance of maintaining up-to-date virtualization software and demonstrates the need for robust memory safety practices in hypervisor implementations, particularly in components that handle hardware abstraction and device management functions.