CVE-2026-47876 in ESX
Summary
by MITRE • 07/30/2026
VMware ESX contains an out-of-bounds write vulnerability in the VMXNET3 virtual network adapter. A malicious actor with local administrative privileges on a virtual machine with VMXNET3 virtual network adapter may exploit this issue to execute code on the host. Non VMXNET3 virtual adapters are not affected by this issue.
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Analysis
by VulDB Data Team • 07/30/2026
This vulnerability represents a critical out-of-bounds write flaw within VMware ESX hypervisor's VMXNET3 virtual network adapter implementation. The issue stems from improper input validation and memory management within the network driver component that handles packet processing for VMXNET3 interfaces. When a malicious actor gains local administrative access to a guest virtual machine configured with a VMXNET3 network adapter, they can craft specifically formatted network packets or manipulate the adapter's internal state to trigger an out-of-bounds memory write operation. This type of vulnerability falls under CWE-787 Out-of-bounds Write which is classified as a high-severity flaw due to its potential for arbitrary code execution. The attack vector requires local administrative privileges within the guest operating system, making it a privilege escalation vulnerability that could be exploited by attackers who have already compromised a virtual machine instance.
The operational impact of this vulnerability extends beyond simple code execution as it fundamentally compromises the isolation properties that hypervisors are designed to maintain between guest operating systems and the host system. When successful, exploitation allows an attacker to execute arbitrary code with the privileges of the host system, effectively breaking down the security boundaries that separate virtual machines from each other and from the underlying infrastructure. This creates a severe risk for multi-tenant environments where multiple organizations share the same physical hardware, as a single compromised guest could potentially allow attackers to access resources belonging to other tenants or even gain control over the entire host server. The vulnerability affects only VMXNET3 adapters because this specific network driver implementation contains the flawed memory handling logic while other virtual network adapter types such as E1000, Vmxnet2, or Paravirtualized adapters do not exhibit this particular weakness.
From a defensive standpoint, organizations must implement immediate mitigations to protect their VMware environments from potential exploitation of this vulnerability. The most effective approach involves updating VMware ESX hypervisor installations to versions that contain patches addressing the VMXNET3 out-of-bounds write issue, as recommended by VMware's security advisories and CVE updates. Additionally, administrators should consider disabling or removing VMXNET3 adapters from virtual machines where they are not strictly required, particularly in environments where guest operating systems may be compromised or untrusted. Network segmentation and monitoring controls should also be enhanced to detect anomalous network behavior that might indicate exploitation attempts. The vulnerability aligns with ATT&CK technique T1059 Command and Scripting Interpreter and T1068 Exploitation for Privilege Escalation, as it enables attackers to execute code on the host system and escalate their privileges beyond the initial guest access level. Security teams should also implement continuous vulnerability scanning processes to identify affected systems and ensure that all virtualization components remain up-to-date with the latest security patches according to industry best practices outlined in NIST SP 800-125 and ISO/IEC 27001 standards for virtualization security controls.