CVE-2026-80676 in Linux
Summary
by MITRE • 08/28/2026
In the Linux kernel, the following vulnerability has been resolved:
Drivers: hv: vmbus: use generic driver_override infrastructure
When a driver is probed through __driver_attach(), the bus' match() callback is called without the device lock held, thus accessing the driver_override field without a lock, which can cause a UAF.
Fix this by using the driver-core driver_override infrastructure taking care of proper locking internally.
Note that calling match() from __driver_attach() without the device lock held is intentional. [1]
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Analysis
by VulDB Data Team • 08/28/2026
The Linux kernel vulnerability identified in the Hyper-V vmbus subsystem represents a classic race condition arising from improper synchronization during driver binding operations. Specifically, when the kernel attempts to probe a driver for a virtual bus device through the __driver_attach function, it invokes the bus match callback. This process is critical for establishing the relationship between hardware devices and their corresponding drivers within the system architecture. However, in this specific implementation, the match callback accesses the driver_override field without holding the necessary device lock. The absence of proper locking mechanisms creates a window where concurrent operations can interfere with each other, leading to memory safety violations that compromise kernel stability and security integrity.
The core technical flaw lies in the unsynchronized access to the driver_override structure member. In Linux kernel development, fields related to dynamic driver binding or override configurations are often subject to modification by multiple threads or contexts simultaneously. Without holding the device lock during this read operation, a race condition emerges where one context might be modifying or freeing the underlying data structures while another is reading them. This scenario directly facilitates a Use-After-Free (UAF) vulnerability. A UAF occurs when program memory that has been freed is still referenced by other parts of the codebase, leading to undefined behavior, potential kernel panics, and potentially arbitrary code execution if an attacker can control the data written into the reclaimed memory region before it is reallocated for a different purpose.
From a threat modeling perspective, this vulnerability aligns with CWE-416, which describes Use After Free errors. The exploitation of such flaws typically requires local access to trigger the race condition during device probing or driver override scenarios. While remote exploitation is less likely due to the specific nature of Hyper-V virtual bus interactions, successful exploitation could allow a privileged user or an attacker who has gained initial foothold within the guest operating system to escalate privileges by crashing the kernel or executing arbitrary code in ring 0 context. This undermines the isolation guarantees provided by the hypervisor and compromises the overall security posture of the virtualized environment.
The mitigation implemented addresses this issue by leveraging the generic driver-core infrastructure for handling driver overrides. By delegating the management of the driver_override field to the core kernel subsystem, the fix ensures that proper locking mechanisms are applied internally during access operations. This approach not only resolves the immediate race condition but also aligns with established best practices in Linux kernel development, reducing code duplication and enhancing consistency across different bus types. The note regarding __driver_attach calling match without the device lock being intentional highlights a design decision where performance or specific architectural constraints necessitated this pattern, making external synchronization via the driver-core infrastructure the correct corrective action rather than altering the fundamental probing logic itself.
Security practitioners should ensure that systems running affected versions of the Linux kernel are updated to include patches from Microsoft and upstream kernel maintainers. For environments utilizing Hyper-V virtualization on Linux guests, verifying the presence of this specific fix in the vmbus driver is essential. Additionally, monitoring for unusual system crashes or stability issues related to device enumeration can serve as an indicator of potential exploitation attempts. Adhering to strict patch management policies and keeping kernel components up to date remains the primary defense against such low-level memory corruption vulnerabilities that exploit synchronization gaps within critical subsystems.