CVE-2023-20870: VMware Fusion Out-of-Bounds Vulnerability

CVE-2023-20870 Overview

VMware Workstation and Fusion contain an out-of-bounds read vulnerability that exists in the functionality for sharing host Bluetooth devices with the virtual machine. This memory safety issue allows a malicious actor with local administrative privileges on a virtual machine to read privileged information contained in hypervisor memory from the virtual machine.

Critical Impact

An attacker with administrative access to a guest VM can exploit this vulnerability to read sensitive hypervisor memory, potentially exposing confidential information from the host system or other virtual machines.

Affected Products

• VMware Workstation
• VMware Fusion

Discovery Timeline

• April 25, 2023 - CVE-2023-20870 published to NVD
• February 4, 2025 - Last updated in NVD database

Technical Details for CVE-2023-20870

Vulnerability Analysis

This vulnerability is classified as an out-of-bounds read (CWE-125) affecting the Bluetooth device sharing functionality between host systems and virtual machines. The flaw resides in how VMware Workstation and Fusion handle memory operations when sharing host Bluetooth devices with guest VMs.

The vulnerability requires local access to the system and high privileges (administrative access on the guest VM) for exploitation. While it cannot be exploited remotely over a network, its scope extends beyond the vulnerable component—meaning a successful attack on a guest VM can impact the host hypervisor memory, creating a potential pathway for information disclosure across VM boundaries.

Root Cause

The root cause stems from improper bounds checking in the Bluetooth device sharing implementation. When the hypervisor processes Bluetooth-related data from a guest VM, it fails to properly validate memory read boundaries. This allows crafted requests from a privileged guest context to access memory locations outside the intended buffer, resulting in the exposure of hypervisor memory contents.

Attack Vector

The attack requires an adversary to first gain administrative privileges within a guest virtual machine. From this position, the attacker can interact with the Bluetooth device sharing functionality in a manner that triggers the out-of-bounds read condition. Since Bluetooth device sharing must be enabled for the vulnerability to be exploitable, configurations without this feature active are not affected.

The exploitation mechanism involves sending specially crafted requests through the Bluetooth sharing interface that cause the hypervisor to read beyond allocated memory boundaries. The leaked data is then accessible to the attacker within the guest VM context, potentially revealing sensitive information from the host hypervisor's memory space.

Detection Methods for CVE-2023-20870

Indicators of Compromise

• Unusual or excessive Bluetooth-related activity between guest VMs and the host system
• Unexpected memory access patterns in VMware hypervisor logs
• Administrative activity on guest VMs followed by abnormal Bluetooth device interactions
• Evidence of information gathering or reconnaissance activities from within guest VMs

Detection Strategies

• Monitor VMware Workstation and Fusion process behavior for anomalous memory access patterns
• Audit administrative logins and privilege escalation events within guest virtual machines
• Enable enhanced logging for Bluetooth device sharing operations when available
• Deploy endpoint detection solutions capable of monitoring hypervisor-level activity

Monitoring Recommendations

• Review VMware logs for unusual Bluetooth device sharing requests or errors
• Implement file integrity monitoring on VMware binaries and configuration files
• Monitor for unauthorized changes to VM configurations, particularly Bluetooth sharing settings
• Correlate guest VM administrative activity with host system security events

How to Mitigate CVE-2023-20870

Immediate Actions Required

• Update VMware Workstation and Fusion to the latest patched versions as specified in VMware Security Advisory VMSA-2023-0008
• Disable Bluetooth device sharing functionality on virtual machines where it is not required
• Review and restrict administrative access to guest virtual machines
• Implement network segmentation to limit access to systems running affected VMware products

Patch Information

VMware has released security patches addressing this vulnerability. Detailed patch information, affected version ranges, and upgrade instructions are available in the official VMware Security Advisory VMSA-2023-0008. Organizations should prioritize applying these updates to all affected VMware Workstation and Fusion installations.

Workarounds

• Disable the Bluetooth device sharing feature in VM settings to eliminate the attack surface
• Remove shared Bluetooth devices from virtual machine configurations until patches can be applied
• Limit administrative privileges within guest VMs to reduce the pool of potential attackers
• Consider using alternative methods for Bluetooth connectivity that do not rely on host device sharing

# Disable Bluetooth sharing in VM configuration file (.vmx)
# Locate your VM's .vmx configuration file and add or modify:
usb.generic.allowHID = "FALSE"
usb.generic.autoconnect = "FALSE"

# Alternatively, remove any Bluetooth device entries from the VM configuration
# and disable the USB controller if Bluetooth sharing is not needed