VMware Workstation and Fusion: Two Flaws Allow Escape from the Virtual Machine

Broadcom recently patched two high-severity vulnerabilities in VMware Workstation and VMware Fusion. Both can allow an attacker with administrative privileges inside a virtual machine to execute code on the host system.

The more critical issue, CVE-2026-59346, has a CVSS score of 9.3 and is caused by an integer overflow. The second, CVE-2026-59347, is a stack-based buffer overflow rated CVSS 8.1.

Versions 25H2 and 26H1 of both products are affected. The fix is included in release 26H1u1, and no alternative workarounds have been identified other than upgrading.

Two Different Paths from the Guest to the Host

The vulnerabilities share a common theme: crossing the security boundary between the guest and the host. Virtualization is intended to isolate software running inside a virtual machine from the system hosting it; under certain conditions, these flaws allow that separation to be bypassed.

For CVE-2026-59346, the attacker must already have local administrative privileges inside the guest. The virtual machine must also use a VMXNET3 virtual network adapter.

The flaw is classified as an integer overflow. In general terms, this type of vulnerability occurs when an arithmetic operation produces a value that cannot be represented within the expected range. The resulting value can corrupt calculations involving sizes, offsets, or memory allocations, creating exploitable conditions.

The specific VMXNET3 processing path containing the flaw, as well as the technical sequence required to trigger it, has not been disclosed. The stated impact, however, is clear: a successful attack can result in arbitrary code execution on the host.

CVE-2026-59347 also requires local administrative privileges inside the virtual machine, but there is no indication that VMXNET3 is required. It is a stack-based buffer overflow, meaning that data is written beyond the boundaries of a memory area allocated on the stack.

Exploitation allows code to run on the host with the privileges of the VMX process associated with the virtual machine. No further details are available about the vulnerable component, the data reaching the buffer, or whether specific configurations are required.

Vulnerable Versions and Available Update

The affected products and branches are:

Product	Listed vulnerable versions	Fixed release
VMware Workstation	25H2, 26H1	26H1u1
VMware Fusion	25H2, 26H1	26H1u1

More granular fixed build numbers have not been disclosed. It is also unclear whether Workstation and Fusion use separate packages or different update paths to reach release 26H1u1.

Administrators should therefore verify the supported distribution channel for each installation rather than relying solely on the commercial version name. After upgrading, they should confirm that the product actually reports the correct release.

Broadcom has not provided any workarounds. Disabling VMXNET3 could reduce exposure to CVE-2026-59346 alone, but it is not presented as an official mitigation and does not address CVE-2026-59347. Installing the update remains the definitive remediation.

Risk Increases When Guests Run Untrusted Code

The two vulnerabilities do not appear to be directly exploitable remotely without access to the virtual machine. An attacker must first obtain local administrative privileges in the guest. This requirement limits the attack surface but does not make the risk negligible.

The most exposed environments include laboratories used to analyze untrusted files or programs, development workstations, shared testing environments, and virtual machines assigned to users other than the host administrator. Malware that has already entered the guest could also attempt to use a second vulnerability to reach the underlying system.

The consequences depend on the privileges obtained on the host. For CVE-2026-59347, the stated level is that of the VMX process. For CVE-2026-59346, the impact is described more broadly as arbitrary code execution on the host, without further clarification about the final security context.

A compromise of the guest-host boundary could expose data and credentials stored outside the virtual machine or enable further lateral movement on the system. These are potential scenarios: no attack chains or evidence describing real-world compromises attributable to the two flaws have been published.

No Public Evidence of Attacks, but the Previous KEV Entries Matter

Broadcom has not reported evidence of in-the-wild exploitation of CVE-2026-59346 or CVE-2026-59347. Both vulnerabilities were reportedly disclosed privately to the vendor.

The two identifiers do not appear in the available extract of CISA’s Known Exploited Vulnerabilities catalog. As a result, no known catalog inclusion date or federal remediation deadline applies to them. This does not confirm that attacks are absent: the available content shows only part of the 26 results associated with VMware.

The vendor’s track record nevertheless warrants attention. More than two dozen VMware vulnerabilities are listed in KEV, which tracks flaws for which evidence of exploitation exists. In addition, CVE-2026-59310, attributed to the same vendor, was added to the catalog on August 18, 2026.

Previous cases directly relevant to desktop virtualization products include three vulnerabilities added to KEV on March 4, 2025, all with a federal remediation deadline of March 25, 2025:

• CVE-2025-22224, CVSS 9.3, affects ESXi and Workstation and enables a guest-to-VMX process escape through a TOCTOU race condition;
• CVE-2025-22225, CVSS 8.2, allows an attacker who controls the VMX process to perform an arbitrary write to the ESXi kernel and was used in ransomware campaigns;
• CVE-2025-22226, CVSS 7.1, affects ESXi, Workstation, and Fusion and allows VMX process memory to be read through an HGFS flaw.

There are also previous cases involving other VMware components. CVE-2024-38812 and CVE-2024-38813, which affect vCenter Server, have been listed in KEV since November 20, 2024, with a deadline of December 11, 2024. CVE-2024-37085, an authentication bypass in ESXi used in ransomware campaigns, was added on July 30, 2024, with a deadline of August 20, 2024.

These cases do not show that the two new vulnerabilities are already under attack. They do demonstrate, however, that VMware flaws capable of compromising isolation or management systems are actively exploited.

Checks to Perform Immediately

The first step is to inventory all VMware Workstation and VMware Fusion installations, including those on development workstations or computers that are not centrally managed.

Administrators should then:

1. identify installations running 25H2 and 26H1;
2. upgrade to release 26H1u1 through the update path supported by Broadcom;
3. determine which virtual machines use VMXNET3 adapters, which are relevant to CVE-2026-59346;
4. prioritize guests in which users or administrative processes run untrusted software;
5. confirm that the update was successfully applied on every host;
6. include previous VMware vulnerabilities listed in KEV in the remediation effort.

No specific indicators of compromise, detection signatures, or dedicated forensic procedures have been published. In their absence, monitoring can focus on anomalous VMX process behavior, unexpected virtual machine crashes, and suspicious host-side execution associated with administrative activity in the guest. These signals do not prove exploitation, but they may justify further investigation.

The operational priority is straightforward: wherever Workstation or Fusion 25H2 and 26H1 are present, upgrade to 26H1u1. With no workaround available, postponing the update leaves both virtual-machine escape paths open.