CVE-2025-41239: 
VMware Workstation vulnerability analysis and mitigation

CVE-2025-41239 is a vSockets information disclosure vulnerability affecting VMware ESXi, Workstation, Fusion, and VMware Tools (Windows only). The flaw stems from the use of uninitialized memory in the vSockets subsystem, allowing a malicious actor with local administrative privileges on a virtual machine to leak memory from processes communicating with vSockets. It was disclosed on July 15, 2025, as part of Broadcom's VMSA-2025-0013 advisory, which also covers three other vulnerabilities (CVE-2025-41236, CVE-2025-41237, CVE-2025-41238). The CVSSv3.1 base score is 7.1 (Important/High) for ESXi/Workstation/Fusion, and 6.2 (Moderate) for VMware Tools on Windows (Broadcom Advisory).

The vulnerability is classified as CWE-908 (Use of Uninitialized Resource), where the vSockets communication layer fails to properly initialize memory buffers before use, potentially exposing residual memory contents to a guest VM attacker (Broadcom Advisory). The attack vector is local, requiring no user interaction, and the scope is changed (S:C) for ESXi/Workstation/Fusion, meaning the impact crosses the VM boundary to affect host-side processes. Exploitation requires local administrative privileges within the guest VM. The vulnerability specifically affects VMware Tools for Windows; Linux and macOS versions of VMware Tools are unaffected. It was independently reported by Corentin BAYET (@OnlyTheDuck) of REverse Tactics working with Pwn2Own/Zero Day Initiative, and Gwangun Jung of THEORI working with Trend Micro Zero Day Initiative (Broadcom Advisory).

Successful exploitation allows a guest VM administrator to leak memory contents from host-side processes that communicate via vSockets, resulting in a high confidentiality impact with no integrity or availability impact. Sensitive data such as cryptographic material, credentials, or other process memory could be exposed from the host or other VMs sharing the vSockets interface. The changed scope means the information disclosure extends beyond the guest VM boundary, potentially enabling further attacks if leaked data contains exploitable secrets (Broadcom Advisory, Qualys ThreatProtect).

CVE-2025-41239 was demonstrated at Pwn2Own Berlin 2025, where researchers earned $340,000 for VMware-related exploits in the broader VMSA-2025-0013 advisory (SecurityWeek, Security Affairs). No public proof-of-concept exploit code specific to CVE-2025-41239 is known to be available, and there is no confirmed evidence of in-the-wild exploitation beyond the controlled Pwn2Own context. The EPSS score is approximately 0.014% (0.000140), indicating a low probability of widespread exploitation in the near term. The vulnerability is not currently listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. A ZDI advisory (ZDI-25-611) has been published referencing this issue (ZDI).

1. Gain local admin access in guest VM: The attacker must first obtain local administrative privileges within a target virtual machine running on a vulnerable VMware ESXi, Workstation, or Fusion host.
2. Identify vSockets usage: Enumerate processes on the guest that communicate via VMware's vSockets (VMCI-based virtual socket) interface, which is used for guest-host communication (e.g., VMware Tools services).
3. Trigger uninitialized memory read: Craft and send specially formed vSockets requests or manipulate the vSockets API to trigger the uninitialized memory condition in the vSockets subsystem, causing the hypervisor or host-side process to return memory buffers containing uninitialized (residual) data.
4. Capture and analyze leaked memory: Read the returned data from the vSockets response to extract residual memory contents from host-side processes, potentially recovering sensitive information such as credentials, keys, or other process data.
5. Leverage disclosed data: Use any recovered sensitive information to facilitate further attacks, such as privilege escalation, lateral movement, or exploitation of other vulnerabilities (Broadcom Advisory, ZDI).

• Process: Unusual or unexpected processes within a guest VM making high-frequency or anomalous vSockets API calls; guest VM processes attempting to read large or repeated vSockets responses.
• Logs: VMware Tools or VMX process logs showing unexpected vSockets connection attempts or errors from guest VMs with administrative accounts; ESXi host logs (vmkernel.log, vmware.log) showing abnormal vSockets activity.
• Network: Unusual inter-VM or guest-to-host communication patterns over VMCI/vSockets that deviate from baseline behavior.
• File System: Presence of unknown scripts or binaries in the guest VM that interact with VMware vSockets or VMCI device interfaces (e.g., /dev/vmci on Linux guests, or VMCI driver interactions on Windows guests).

Broadcom has released patches for all affected products; no workarounds are available. Apply the following fixed versions as soon as possible (Broadcom Advisory):

• ESXi 7.0: Update to ESXi70U3w-24784741
• ESXi 8.0: Update to ESXi80U3f-24784735 or ESXi80U2e-24789317
• VMware Workstation 17.x: Update to 17.6.4
• VMware Fusion 13.x: Update to 13.6.4
• VMware Tools 13.x (Windows): Update to 13.0.1.0
• VMware Tools 11.x/12.x (Windows): Update to 12.5.3
• VMware Cloud Foundation 5.x/4.5.x: Apply async ESXi patches per KB88287

Note: VMware Tools for Linux and macOS are unaffected. Additionally, restrict local administrative access to virtual machines and audit guest VM administrator accounts to reduce the attack surface.

The broader VMSA-2025-0013 advisory (which includes CVE-2025-41239) received significant attention due to its connection to Pwn2Own Berlin 2025, where researchers earned $340,000 exploiting VMware products (SecurityWeek). BleepingComputer and Security Affairs covered the advisory prominently, framing the four CVEs as zero-days patched following the competition (BleepingComputer). Reddit communities (r/vmware, r/sysadmin) discussed the advisory with urgency, particularly around the critical-rated companion vulnerabilities. Multiple national CERTs (Canada, Singapore, Belgium, Hong Kong) issued advisories recommending prompt patching. CVE-2025-41239 itself attracted less individual attention than the critical-rated code execution flaws in the same advisory, but was noted as part of the overall patch priority.