CVE-2026-77178 in VM VirtualBox
Summary
by MITRE • 10/06/2026
Oracle VM VirtualBox before 7.2.8 allows guest OS users to cause an out-of-bounds write in the host OS in pcnetReceiveNoSync in DevPCNet.cpp in the PCNet (Am79C970A) network device model.
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Analysis
by VulDB Data Team • 10/06/2026
The vulnerability identified in Oracle VM VirtualBox prior to version 7.2.8 represents a critical security flaw within the emulation of the Am79C970A network adapter, specifically located in the pcnetReceiveNoSync function found in DevPCNet.cpp. This component is responsible for handling incoming network packets from the virtualized guest environment and processing them into a format suitable for the host operating system's networking stack. The core technical flaw involves an out-of-bounds write condition that occurs when the hypervisor processes malformed or maliciously crafted packet data sent by a privileged user within the guest OS. Because VirtualBox operates with elevated privileges on the host machine to manage virtual hardware, any memory corruption in this layer can have severe consequences for system stability and security.
From an operational perspective, this vulnerability allows a guest operating system user who has access to the network interface of the virtual machine to trigger a buffer overflow within the host's memory space. By carefully crafting packet headers or payload data that exceeds expected bounds while bypassing existing validation checks in the pcnetReceiveNoSync routine, an attacker can write arbitrary data to adjacent memory locations on the host system. This type of out-of-bounds write is particularly dangerous because it does not necessarily cause an immediate crash but rather corrupts internal data structures used by the hypervisor or other processes running on the host machine. Such corruption can lead to unpredictable behavior, including denial of service conditions where the VirtualBox process crashes, potentially affecting all virtual machines hosted on that instance.
More critically, this memory corruption vulnerability serves as a potential pathway for privilege escalation and arbitrary code execution on the host system. If an attacker can control the content written beyond the buffer boundaries, they may overwrite function pointers or return addresses within the hypervisor's memory space. This technique aligns with common exploitation strategies documented in industry standards such as CWE-787: Out-of-bounds Write. By manipulating these overwritten values, a malicious guest user could potentially execute arbitrary code with the privileges of the VirtualBox process on the host OS. This effectively breaks the isolation boundary between the virtual machine and the physical hardware, allowing the attacker to gain control over the underlying system infrastructure.
The classification of this vulnerability also relates closely to ATT&CK technique T1059: Command and Scripting Interpreter if exploitation leads to code execution, or more broadly to lateral movement techniques within a compromised environment where the host is used as a pivot point for further attacks against other systems on the network. The lack of proper bounds checking in the PCNet device model highlights a gap in input validation practices during packet processing. This specific flaw underscores the risks associated with complex emulation layers that must translate guest instructions into host operations without sufficient sanitization of external inputs.
To mitigate this risk, organizations running Oracle VM VirtualBox must immediately upgrade to version 7.2.8 or later, where these bounds checking mechanisms have been corrected and validated by security engineers. In environments where upgrading is not immediately feasible, strict network segmentation policies should be enforced to limit the exposure of virtual machines with active network interfaces to untrusted networks. Additionally, running VirtualBox processes under restricted user accounts rather than administrative privileges can help contain the potential impact of a successful exploitation attempt, although it does not eliminate the vulnerability itself. Regular patching cycles and monitoring for anomalous behavior in hypervisor resource usage are essential components of a defense-in-depth strategy against such guest-to-host escape vulnerabilities.