External risk intelligence

Oracle VM VirtualBox PCNet Out-of-Bounds Write Vulnerability.

CVE advisorySeverity: CRITICAL (CVSS 9.1)

CVE-2026-77178

This vulnerability exists within the PCNet network device model of a virtual machine monitor (VirtualBox). Exploitation requires a user to already have access to the guest OS. This is a local virtualization component not intended for direct exposure to the public internet, and it is typically restricted to the host-guest boundary within isolated desktop or server virtualization environments.

Out-of-bounds Write

Halo Surface Signal: 1 out of 5 — much less likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A vulnerability has been identified in Oracle's VirtualBox software that could allow someone with access to a virtual machine to potentially impact the host system. The issue resides within the network device model of the virtual machine.

Guest users can write outside allowed memory.
Confirms a potential risk to host systems.
Verify relevance and assess exposure level.

Attack Path

How an attacker could exploit the issue

An attacker could exploit this vulnerability by leveraging access within a virtual machine's guest operating system. This would allow them to target the PCNet network device model, leading to an out-of-bounds write on the host operating system. The vulnerability is present in the PCNet network device model within Oracle VM VirtualBox.

Guest OS access required.
Vulnerable PCNet device model.
Host OS corruption possible.

Live Threat

Current exploitation, exposure, and threat context

Guest operating system users could trigger an out-of-bounds write vulnerability in the host operating system through the PCNet network device model when running VirtualBox before version 7.2.8.

Host operating system integrity.
Malicious input via network device model.
Potential host system compromise.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability in VirtualBox's PCNet network device model requires guest OS access, making it a concern for teams managing virtualization platforms. The first step is to confirm which hosts run VirtualBox, assess if guest VMs are exposed to untrusted networks, and identify the accountable owner for remediation or mitigation.

Virtualization or platform teams own the issue.
Verify guest OS access and network exposure.
Plan VM host patching or network segmentation.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is Oracle VM VirtualBox?

Oracle VM VirtualBox is a hypervisor that enables users to run multiple, independent operating systems simultaneously on a single physical host machine. It provides simulated hardware components, such as network adapters and storage controllers, allowing a guest operating system to function as if it were running on its own dedicated hardware.

What does CVE-2026-77178 mean?

This CVE identifies an out-of-bounds write vulnerability, classified as CWE-787. It means the software fails to properly restrict memory access when processing data within its simulated PCNet network hardware. Because the code writes data beyond the intended buffer, it could allow a guest environment to affect the host's memory integrity.

How is this vulnerability triggered?

An attacker must already have control over a guest operating system to interact with the virtualized PCNet device model. Simply browsing the internet or visiting a malicious website on the host machine does not trigger this bug; the malicious input must originate from within the virtualized guest environment itself.

Is my system at risk for CVE-2026-77178?

Halo Surface Signal notes that this vulnerability exists within a virtualized network device and typically requires local access to a guest virtual machine. Since this component is not designed for direct exposure to the public internet and operates primarily within the host-guest boundary, it is generally considered unlikely to be reachable from the internet.

Do I need to update my software?

Yes, you should identify all systems running VirtualBox versions prior to 7.2.8. Your primary step is to verify which hosts are running this software and evaluate the trust level of the guest virtual machines they host. Coordinating with your virtualization team to plan for an upgrade to a patched version is the recommended path forward.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.