CVE-2025-41237 Overview
CVE-2025-41237 is a critical integer-underflow vulnerability in the Virtual Machine Communication Interface (VMCI) component of VMware ESXi, Workstation, and Fusion. This vulnerability results in an out-of-bounds write condition that can be exploited by a malicious actor with local administrative privileges on a virtual machine to execute code as the virtual machine's VMX process running on the host system.
The impact varies by product: on ESXi, exploitation is contained within the VMX sandbox, providing some isolation. However, on Workstation and Fusion, successful exploitation may lead to arbitrary code execution on the host machine where the virtualization software is installed, representing a complete virtual machine escape scenario.
Critical Impact
VM escape vulnerability allowing code execution on the host system from within a guest virtual machine with administrative privileges.
Affected Products
- VMware ESXi
- VMware Workstation
- VMware Fusion
Discovery Timeline
- July 15, 2025 - CVE-2025-41237 published to NVD
- July 15, 2025 - Last updated in NVD database
Technical Details for CVE-2025-41237
Vulnerability Analysis
This vulnerability is classified under CWE-787 (Out-of-bounds Write), stemming from an integer underflow condition within the VMCI component. The VMCI serves as a high-speed communication interface between virtual machines and the host, as well as between virtual machines themselves. Due to the privileged nature of this component and its direct interaction with host memory structures, vulnerabilities in VMCI can have severe security implications.
The integer underflow occurs when processing specific VMCI operations, causing a calculation to wrap around to an unexpectedly large value. This incorrect value is then used to determine memory boundaries, resulting in an out-of-bounds write operation that can corrupt adjacent memory regions.
Root Cause
The root cause lies in improper handling of arithmetic operations within the VMCI subsystem. When certain input values are processed without adequate validation, an integer underflow can occur. This happens when a subtraction operation produces a result smaller than the minimum value the integer type can hold, causing the value to wrap around to the maximum representable value. The resulting corrupted length or offset value leads to memory writes outside the intended buffer boundaries.
Attack Vector
This vulnerability requires local access with administrative privileges within a guest virtual machine. An attacker who has compromised or controls a virtual machine with admin rights can craft malicious VMCI requests designed to trigger the integer underflow condition. The attack flow involves:
- Attaining administrative privileges within a guest VM
- Crafting specific VMCI operations with carefully chosen parameters to trigger the underflow
- Exploiting the resulting out-of-bounds write to corrupt VMX process memory
- Achieving code execution in the context of the VMX process on the host
On ESXi systems, the VMX sandbox provides an additional security boundary. On Workstation and Fusion, successful exploitation grants direct code execution on the host operating system, effectively breaking out of the virtual machine isolation.
The vulnerability mechanism involves improper integer arithmetic validation in VMCI operations that process size or offset parameters. When exploited, the underflow causes memory writes to extend beyond allocated buffer boundaries, potentially overwriting critical process structures. For complete technical details, refer to the Broadcom Security Advisory.
Detection Methods for CVE-2025-41237
Indicators of Compromise
- Unusual VMCI-related activity or errors in VMware logs
- Unexpected crashes or restarts of VMX processes
- Anomalous memory access patterns in virtualization host systems
- Signs of privilege escalation within guest virtual machines
Detection Strategies
- Monitor VMware log files for VMCI-related error messages or anomalous activity
- Implement host-based intrusion detection to identify unexpected process behavior from VMX processes
- Deploy endpoint detection and response (EDR) solutions capable of detecting VM escape attempts
- Audit administrative access within guest virtual machines
Monitoring Recommendations
- Enable verbose logging for VMware components to capture VMCI-related events
- Implement real-time alerting for VMX process anomalies or unexpected terminations
- Monitor for signs of lateral movement from virtualized environments to host systems
- Regularly review guest VM administrative access logs for suspicious activity
How to Mitigate CVE-2025-41237
Immediate Actions Required
- Apply the latest security patches from Broadcom/VMware immediately
- Restrict administrative access within guest virtual machines to trusted personnel only
- Review and limit which VMs have VMCI enabled if not required for operations
- Implement network segmentation to limit potential lateral movement from compromised hosts
Patch Information
Broadcom has released security patches addressing this vulnerability. Administrators should consult the Broadcom Security Advisory #35877 for specific patch versions and download links for affected VMware products.
Workarounds
- Disable VMCI on virtual machines where the feature is not required for operations
- Implement strict access controls limiting administrative privileges within guest VMs
- Use VMware security hardening guides to minimize attack surface on virtualization infrastructure
- Consider isolating high-risk workloads to dedicated hosts with enhanced monitoring
# Example: Disable VMCI for a specific VM (add to .vmx file)
vmci0.present = "FALSE"
# Verify VMCI status on ESXi host
esxcli system module list | grep vmci
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
