CVE-2020-3950: VMware Fusion Privilege Escalation Flaw

CVE-2020-3950 Overview

CVE-2020-3950 is a privilege escalation vulnerability affecting VMware Fusion, VMware Remote Console (VMRC) for Mac, and Horizon Client for Mac. The vulnerability stems from improper use of setuid binaries within these applications, allowing attackers with normal user privileges to escalate their privileges to root on affected macOS systems.

This vulnerability is particularly concerning as it allows local attackers to gain complete control over the affected system. Once exploited, an attacker can execute arbitrary commands as root, potentially leading to full system compromise, data theft, or lateral movement within enterprise environments.

Critical Impact

This vulnerability is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, indicating active exploitation in the wild. Organizations running affected VMware products on macOS should prioritize patching immediately.

Affected Products

• VMware Fusion 11.x before 11.5.2
• VMware Remote Console for Mac 11.x and prior before 11.0.1
• Horizon Client for Mac 5.x and prior before 5.4.0
• Apple macOS (as the underlying operating system)

Discovery Timeline

• 2020-03-17 - CVE-2020-3950 published to NVD
• 2025-10-30 - Last updated in NVD database

Technical Details for CVE-2020-3950

Vulnerability Analysis

CVE-2020-3950 exploits a fundamental weakness in how the affected VMware products handle privileged operations on macOS. The vulnerability resides in setuid binaries that are installed as part of VMware Fusion, VMRC, and Horizon Client. Setuid binaries are executable files that run with the permissions of the file owner rather than the user executing them—in this case, running with root privileges.

The improper implementation of these setuid binaries creates an exploitable condition where a local attacker can manipulate the execution flow or input parameters to execute arbitrary code with elevated privileges. This represents a classic privilege escalation scenario where standard user accounts can gain root-level access.

The impact of successful exploitation is severe: complete compromise of the affected macOS system. An attacker can install persistent backdoors, access sensitive data, modify system configurations, and potentially use the compromised system as a pivot point for further attacks within the network.

Root Cause

The root cause of this vulnerability is improper privilege management (CWE-269) in the implementation of setuid binaries within the affected VMware products. Specifically, these privileged binaries fail to properly validate inputs, sanitize the execution environment, or restrict their functionality when called by unprivileged users.

Setuid binaries require careful implementation to prevent privilege escalation attacks. Common issues include:

• Failure to properly drop privileges when performing non-privileged operations
• Unsafe handling of environment variables or command-line arguments
• Improper file path handling allowing symlink attacks
• Race conditions in privilege transitions

Attack Vector

The attack vector for CVE-2020-3950 is local, meaning an attacker must have access to the target macOS system with a standard user account. The exploitation mechanism involves interacting with the vulnerable setuid binaries in a way that causes them to execute attacker-controlled code or commands with root privileges.

The attack does not require user interaction beyond the initial local access. Technical details published on Packet Storm Security indicate that specific setuid binaries, such as the USB Arbitrator component in VMware Fusion, can be manipulated to achieve privilege escalation.

For technical exploitation details, refer to the Packet Storm security advisories and the VMware Security Advisory VMSA-2020-0005.

Detection Methods for CVE-2020-3950

Indicators of Compromise

• Unexpected processes running as root spawned from VMware Fusion, VMRC, or Horizon Client binaries
• Unusual modifications to system files or user privilege escalation events in system logs
• Suspicious activity involving setuid binaries in /Applications/VMware Fusion.app/ or related VMware installation paths
• Anomalous authentication events showing privilege changes for standard user accounts
• New root-owned files or processes appearing in non-standard locations following VMware binary execution

Detection Strategies

• Monitor process execution chains for VMware binaries spawning unexpected child processes with elevated privileges
• Implement file integrity monitoring on VMware installation directories to detect unauthorized modifications
• Review macOS unified logs for privilege escalation patterns using log show --predicate 'eventMessage CONTAINS "privilege"'
• Deploy endpoint detection rules to identify known exploitation patterns associated with CVE-2020-3950
• Use SentinelOne's behavioral AI to detect anomalous privilege transitions from standard user to root context

Monitoring Recommendations

• Enable detailed audit logging on macOS systems running affected VMware products
• Configure SentinelOne to alert on suspicious setuid binary execution patterns
• Monitor network traffic for signs of post-exploitation activity such as command-and-control communications
• Establish baseline behavior profiles for VMware applications to identify deviations

How to Mitigate CVE-2020-3950

Immediate Actions Required

• Update VMware Fusion to version 11.5.2 or later immediately
• Update VMware Remote Console for Mac to version 11.0.1 or later
• Update Horizon Client for Mac to version 5.4.0 or later
• Review system logs for evidence of exploitation attempts prior to patching
• Conduct privilege audits on macOS systems where affected software was installed

Patch Information

VMware has released security updates addressing this vulnerability as documented in VMSA-2020-0005. The following versions contain the fix:

Organizations should download and apply updates from the official VMware download portal. Given the confirmed exploitation in the wild (CISA KEV listing), emergency patching procedures are recommended.

Workarounds

• Restrict local access to systems running vulnerable VMware products to trusted administrators only
• Consider temporarily removing or disabling affected VMware products if patching is not immediately feasible
• Implement application whitelisting to prevent unauthorized binaries from executing with elevated privileges
• Monitor setuid binaries on affected systems using macOS system integrity protection features
• Deploy additional endpoint monitoring to detect privilege escalation attempts

# Verify installed VMware Fusion version
/Applications/VMware\ Fusion.app/Contents/Library/vmware-vmx --version

# List setuid binaries in VMware installation directory (for audit purposes)
find /Applications/VMware\ Fusion.app -perm -4000 -type f 2>/dev/null

# Check for VMRC version
mdls -name kMDItemVersion /Applications/VMware\ Remote\ Console.app