CVE-2025-41239: VMware vSockets Information Disclosure

CVE-2025-41239 Overview

CVE-2025-41239 is an information disclosure vulnerability affecting VMware ESXi, Workstation, Fusion, and VMware Tools. The vulnerability exists due to the usage of uninitialized memory in vSockets, a communication mechanism that enables efficient data transfer between virtual machines and their host systems. A malicious actor with local administrative privileges on a virtual machine may be able to exploit this issue to leak memory from processes communicating with vSockets.

Critical Impact

Attackers with administrative access to a guest VM can potentially extract sensitive data from host memory processes, potentially compromising confidential information across the virtualization boundary.

Affected Products

• VMware ESXi
• VMware Workstation
• VMware Fusion
• VMware Tools

Discovery Timeline

• July 15, 2025 - CVE-2025-41239 published to NVD
• July 15, 2025 - Last updated in NVD database

Technical Details for CVE-2025-41239

Vulnerability Analysis

This vulnerability falls under CWE-908: Use of Uninitialized Resource. When vSockets are utilized for inter-process communication between virtual machines and the host, certain memory buffers are not properly initialized before use. This creates a condition where residual data from previous memory allocations can be inadvertently exposed to processes on the guest VM.

The attack requires local administrative privileges on the virtual machine, meaning an attacker must first compromise or have legitimate access to a guest VM with elevated permissions. From this position, the attacker can craft specific vSocket operations that cause the VMware virtualization layer to return uninitialized memory contents, potentially containing sensitive information from other processes or the host system.

Root Cause

The root cause of CVE-2025-41239 is improper memory initialization within the vSockets implementation. When memory buffers are allocated for vSocket communications, they retain data from their previous use rather than being zeroed out or initialized to safe values. This memory hygiene failure allows information to leak across trust boundaries in the virtualization stack.

Attack Vector

The attack vector for this vulnerability is local, requiring the attacker to have administrative privileges on a guest virtual machine. The exploitation flow involves:

1. An attacker gains local administrative access to a guest VM running on an affected VMware hypervisor
2. The attacker initiates vSocket communication requests designed to trigger allocation of uninitialized memory buffers
3. The VMware virtualization layer returns data in these buffers without proper initialization
4. The attacker reads the returned data, which may contain sensitive information from host memory or other process contexts

The vulnerability allows for high confidentiality impact as memory contents from processes communicating via vSockets can be exposed, though it does not directly enable integrity violations or availability disruptions.

Detection Methods for CVE-2025-41239

Indicators of Compromise

• Unusual vSocket connection patterns originating from guest VMs with administrative sessions
• Unexpected volume of vSocket operations from individual virtual machines
• Anomalous memory access patterns within VMware processes handling vSocket communications
• Evidence of data exfiltration attempts from guest VMs targeting host-level information

Detection Strategies

• Monitor VMware logs for unusual vSocket activity, particularly from VMs with administrative users
• Implement behavioral analysis to detect abnormal inter-VM communication patterns
• Deploy endpoint detection on guest VMs to identify privilege escalation attempts that could precede exploitation
• Enable verbose logging on VMware ESXi hosts to capture detailed vSocket transaction data

Monitoring Recommendations

• Configure SIEM rules to alert on anomalous vSocket traffic volumes from individual guest VMs
• Establish baseline vSocket communication patterns and alert on deviations
• Monitor for processes attempting to read large amounts of data through vSocket interfaces
• Implement network segmentation monitoring between VM tiers to detect lateral movement attempts

How to Mitigate CVE-2025-41239

Immediate Actions Required

• Review the Broadcom Security Advisory #35877 for specific patch details and affected version information
• Limit administrative access to guest virtual machines to essential personnel only
• Audit current VM administrative accounts and remove unnecessary elevated privileges
• Implement network isolation for sensitive VMs pending patch deployment

Patch Information

VMware has released security patches to address this vulnerability. Organizations should consult the Broadcom Security Advisory #35877 for specific version numbers and patch download information for VMware ESXi, Workstation, Fusion, and VMware Tools. Apply patches according to your organization's change management procedures, prioritizing production environments with sensitive workloads.

Workarounds

• Restrict administrative access on guest VMs to only trusted personnel with legitimate need
• Consider disabling vSockets on VMs where this communication mechanism is not required for business operations
• Implement additional monitoring on VMs with administrative users to detect potential exploitation attempts
• Deploy network segmentation to limit potential data exfiltration paths from compromised VMs
• Enable enhanced logging on ESXi hosts to improve forensic capabilities

# Example: Verify VMware Tools version on ESXi host
esxcli software vib list | grep -i tools

# Example: Check current ESXi version for patch assessment
vmware -v