CVE-2026-108399 in Windows
Summary
by MITRE • 10/14/2026
Heap-based buffer overflow in Windows Hyper-V allows an authorized attacker to elevate privileges locally.
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Analysis
by VulDB Data Team • 10/14/2026
The vulnerability described constitutes a critical security flaw within the Microsoft Windows Hypervisor, specifically affecting the virtualization infrastructure known as Hyper-V. This component is responsible for managing hardware resources and isolating guest operating systems from the host environment. The core technical issue is identified as a heap-based buffer overflow, which occurs when data written to a dynamically allocated memory region exceeds its designated boundaries. In this specific context, an attacker who has already gained authorized access to the local system can exploit this flaw by triggering malformed operations within the Hyper-V stack. Because the vulnerability resides in a privileged component of the operating system kernel, successful exploitation allows the attacker to execute arbitrary code with elevated privileges, effectively bypassing standard security controls and gaining control over the host machine.
From a technical perspective, heap-based buffer overflows are particularly dangerous because they can corrupt memory management structures such as allocation metadata or function pointers stored in adjacent memory blocks. When an authorized user interacts with vulnerable Hyper-V components, potentially through specific API calls or virtualized device interactions, improper bounds checking allows for the writing of excessive data onto the heap. This overflow condition enables the attacker to overwrite critical memory locations, leading to a change in program execution flow. By carefully crafting the payload, the attacker can redirect control to malicious shellcode injected into the process space. Since Hyper-V operates at Ring 0 or equivalent high-privilege levels depending on the specific implementation and virtualization extensions used, compromising this component grants full administrative access to the underlying host operating system, regardless of the privilege level of the initial user account that triggered the exploit.
The operational impact of this vulnerability is severe due to its potential for local privilege escalation. An attacker with low-level credentials can leverage this flaw to achieve SYSTEM or root-equivalent privileges on the Windows host. This transformation from a standard user to an administrator fundamentally breaks the principle of least privilege and undermines system integrity. Once elevated, the attacker can install persistent backdoors, steal sensitive data such as cryptographic keys or passwords stored in memory, disable security software including antivirus and endpoint detection systems, and pivot to other machines on the network if the host serves as a gateway or domain controller. Furthermore, because Hyper-V is often used in enterprise environments for hosting critical virtualized workloads, compromising the hypervisor can lead to the compromise of all guest VMs running on that host, resulting in widespread data breaches and service disruptions across multiple tenants or departments.
In terms of industry classification standards, this vulnerability aligns with Common Weakness Enumeration (CWE) ID 120, which describes a buffer overflow without specification of memory type, specifically falling under the sub-category of heap-based overflows where dynamic allocation is involved. It also maps to MITRE ATT&CK techniques related to privilege escalation and defense evasion, particularly those involving exploitation of system services or kernel modules for lateral movement and persistence within an enterprise environment. The attack vector requires local access with authentication, classifying it as a Local Privilege Escalation (LPE) vulnerability rather than a remote code execution flaw, which necessitates that the attacker already have some form of foothold on the target machine.
Mitigation strategies must focus primarily on applying vendor-provided security patches to update the Windows Hyper-V components and related hypervisor drivers. Organizations should prioritize patching systems running vulnerable versions of Windows Server or client operating systems with Hyper-V enabled, especially those exposed to untrusted users or multi-tenant environments. In addition to patching, implementing strict access controls is essential; administrators should enforce least privilege principles by ensuring that only trusted personnel have local administrative rights on hosts running critical virtualization workloads. Network segmentation can also help contain the blast radius if a host is compromised, preventing lateral movement from the hypervisor layer to other network segments. Regular vulnerability scanning and monitoring for anomalous behavior in system processes related to Hyper-V services can aid in early detection of exploitation attempts before full compromise occurs.