CVE-2023-20872: VMware Fusion Buffer Overflow Vulnerability

CVE-2023-20872 Overview

VMware Workstation and Fusion contain an out-of-bounds read/write vulnerability in SCSI CD/DVD device emulation. This memory corruption flaw exists within the virtualization layer that handles SCSI CD/DVD device emulation, allowing attackers with local access to potentially execute arbitrary code with elevated privileges or escape the virtual machine sandbox.

Critical Impact

A malicious actor with local administrative privileges on a virtual machine may exploit this vulnerability to execute code as the virtual machine's VMX process running on the host system, potentially leading to full host compromise.

Affected Products

• VMware Workstation 17.0.0
• VMware Fusion 13.0.0
• Apple macOS (as host operating system for VMware Fusion)

Discovery Timeline

• April 25, 2023 - CVE-2023-20872 published to NVD
• February 4, 2025 - Last updated in NVD database

Technical Details for CVE-2023-20872

Vulnerability Analysis

This vulnerability is classified as CWE-787 (Out-of-bounds Write), a memory corruption vulnerability affecting the SCSI CD/DVD device emulation component in VMware virtualization products. The flaw occurs when the hypervisor improperly handles memory boundaries during SCSI device operations, allowing read and write operations beyond allocated buffer limits.

The vulnerability is exploitable locally, requiring the attacker to have access to a virtual machine running on the affected host. With low privilege requirements and no user interaction needed, an attacker who gains initial access to a VM can leverage this vulnerability to break out of the virtualized environment. The scope change indicator demonstrates that successful exploitation affects resources beyond the vulnerable component—specifically, the host system running the VMware hypervisor.

Root Cause

The root cause stems from improper bounds checking within the SCSI CD/DVD device emulation code path. When processing certain SCSI commands, the emulation layer fails to properly validate input parameters against buffer boundaries, resulting in out-of-bounds memory access. This allows an attacker to read or write memory locations outside the intended buffer, potentially corrupting critical data structures or injecting malicious code into the VMX process.

Attack Vector

The attack requires local access to a virtual machine running on a vulnerable VMware Workstation or Fusion installation. An attacker with administrative privileges within the guest operating system can craft malicious SCSI commands directed at the emulated CD/DVD device. These specially crafted commands trigger the out-of-bounds read/write condition, enabling memory corruption in the host's VMX process.

The exploitation flow involves:

1. Attacker gains local administrative access to a guest virtual machine
2. Attacker interacts with the SCSI CD/DVD device through specially crafted SCSI commands
3. The malformed commands bypass bounds checking in the emulation layer
4. Memory corruption occurs in the VMX process running on the host
5. Code execution is achieved in the context of the VMX process, potentially escaping the VM sandbox

Detection Methods for CVE-2023-20872

Indicators of Compromise

• Unusual SCSI command sequences targeting CD/DVD devices in VM logs
• Unexpected crashes or restarts of VMX processes on the host
• Abnormal memory allocation patterns in VMware process space
• Suspicious activity originating from VM processes attempting host-level operations

Detection Strategies

• Monitor VMware host logs for unexpected VMX process terminations or error conditions
• Implement endpoint detection rules to identify anomalous SCSI device interactions from guest VMs
• Deploy behavioral analysis to detect virtual machine escape attempts
• Use memory integrity monitoring on VMware host systems to detect corruption patterns

Monitoring Recommendations

• Enable verbose logging for SCSI device emulation in VMware products
• Configure SIEM rules to alert on VMX process crashes or unexpected behavior
• Monitor for privilege escalation attempts following VM-based activity
• Implement host-based intrusion detection focused on VMware process integrity

How to Mitigate CVE-2023-20872

Immediate Actions Required

• Update VMware Workstation to version 17.0.2 or later
• Update VMware Fusion to version 13.0.2 or later
• Remove CD/DVD devices from virtual machine configurations when not required
• Restrict administrative access to virtual machines to trusted users only

Patch Information

VMware has released security patches addressing this vulnerability as documented in VMware Security Advisory VMSA-2023-0008. Organizations should prioritize updating to the patched versions of VMware Workstation (17.0.2 or later) and VMware Fusion (13.0.2 or later) to remediate this vulnerability.

Workarounds

• Remove the SCSI CD/DVD device from virtual machines to eliminate the attack surface
• Use only trusted virtual machine images and restrict VM administrative access
• Implement network segmentation to limit lateral movement if VM escape occurs
• Apply defense-in-depth measures on host systems to detect and prevent post-exploitation activity

As a temporary workaround, administrators can remove the CD/DVD device from affected virtual machines through the VM settings. This can be accomplished via the VMware interface by editing the virtual machine configuration and removing the CD/DVD drive component, or by modifying the .vmx configuration file to remove SCSI CD/DVD device entries.