CVE-2026-47876: VMware ESXi VMXNET3 Out-of-Bounds Write Virtual Machine Escape

HERMES

HERMES THREAT SCORE & HYPERVISOR ESCAPE PROFILE

Target: VMware ESXi VMXNET3 Emulated Network Controller (vmx / VMkernel)

Confidence: 98%

94 / 100

CRITICAL

Measures real-world operational relevance, exploit weaponization, and active threat posture.

Dimension Breakdown

Exploitability 19 / 20

Threat Activity 18 / 20

Weaponization 19 / 20

Exposure 18 / 20

Prevalence 20 / 20

Impact 20 / 20

Exploit Maturity 18 / 20

Attack Chain Potential 20 / 20

⚖️ Divergence & Operational Rationale

Hermes evaluates CVE-2026-47876 at Critical severity (HTS 94). Hypervisor escapes break the ultimate isolation barrier in virtualized environments. An attacker possessing local administrative or root rights inside a guest virtual machine can compromise the underlying ESXi hypervisor, jeopardizing all collocated enterprise workloads.

🕸️ Connected Knowledge Graph & Provenance

CVE-2026-47876: VMware ESXi VMXNET3 Out-of-Bounds Write Virtual Machine EscapeVULNERABILITY

Connected Nodes: 0

Critical Virtual Machine Escape in VMXNET3

CVSS v3.1: 8.5 High / 9.0 Adjusted (CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H) / CWE-787: Out-of-bounds Write.
Disclosed in VMware advisory VMSA-2026-0006. An out-of-bounds write flaw in the VMXNET3 virtual network adapter emulation allows a local guest administrator to write arbitrary memory into the host vmx process, escaping the guest boundary and executing code on the ESXi host. Fixed in ESXi 8.0U3, ESXi 7.0U3q, Workstation 17.6, and Fusion 13.6.

Executive Summary

Broadcom / VMware published security advisory VMSA-2026-0006 detailing CVE-2026-47876, a high-impact hypervisor escape vulnerability in ESXi and desktop hypervisors.

VMXNET3 is VMware’s flagship para-virtualized network driver, designed for high-throughput packet delivery between guest OS kernels and the ESXi VMkernel. By submitting crafted receive/transmit ring descriptor buffers, a guest operating system bypasses bounds checking and corrupts host memory heap pointers.

---

1. Metadata & Attack Surface

Metric	Technical Specification	Operational Impact
CVE Identifier	CVE-2026-47876	Standardized vulnerability identifier
Vendor / Advisory	VMware by Broadcom / VMSA-2026-0006	Official security bulletin
Affected Products	VMware ESXi, Workstation Pro, Fusion	Enterprise hypervisors
Affected Releases	ESXi 8.0 < 8.0U3, ESXi 7.0 < 7.0U3q	Multi-version virtual infrastructure
Fixed Releases	ESXi 8.0U3, ESXi 7.0U3q, WS 17.6, Fusion 13.6	Hypervisor patch releases
Associated CWE	CWE-787: Out-of-bounds Write	Memory safety corruption
Access Vector	Local Guest Administrator (AV:L/PR:H)	Guest VM superuser
Escalation Result	Hypervisor Host Execution (Scope: Changed)	Complete hypervisor host takeover

---

2. Technical Root Cause Analysis

The flaw exists within the VMXNET3 device emulation module inside the ESXi host vmx process:

CVE-2026-47876 Hypervisor Escape Chain:

  ┌────────────────────────────────────────────────────────┐
  │ Guest Virtual Machine (Compromised Admin)              │
  └───────────────────────────┬────────────────────────────┘
                              │
                              │ Malformed VMXNET3 ring descriptors with
                              │ out-of-spec packet chunk offsets
                              ▼
  ┌────────────────────────────────────────────────────────┐
  │ ESXi Host vmx Process (VMXNET3 Device Emulation)       │
  │ - Ingests descriptor packet boundaries without checks  │
  │ - Overwrites memory outside allocated DMA ring buffers │
  └───────────────────────────┬────────────────────────────┘
                              │
                              ▼
  ┌────────────────────────────────────────────────────────┐
  │ Host Memory Hijack & Arbitrary Code Execution          │
  │ - Corrupts function dispatch tables                    │
  │ - Executes arbitrary machine instructions on ESXi host │
  └────────────────────────────────────────────────────────┘

When packet assembly logic encounters oversized multi-buffer descriptors, arithmetic overflow in index calculation permits writing data outside the boundaries of the assigned host buffer.

---

3. Remediation & Hardening Playbook

1. Apply ESXi Hypervisor Patches:
   Update all standalone and vCenter-managed ESXi hosts to ESXi 8.0 Update 3 or ESXi 7.0 Update 3q.
2. Temporary Mitigation (Hardware Adapter Fallback):
   If patching cannot be performed immediately, virtual machines can be reconfigured with standard E1000E virtual network adapters instead of VMXNET3 (note: performance penalty may occur).
3. Restrict Guest Administrative Privileges:
   Audit guest VM access controls to prevent untrusted users from gaining kernel-level rights inside tenant VMs.