CVE-2025-40211 in Linux
Summary
by MITRE • 11/21/2025
In the Linux kernel, the following vulnerability has been resolved:
ACPI: video: Fix use-after-free in acpi_video_switch_brightness()
The switch_brightness_work delayed work accesses device->brightness and device->backlight, freed by acpi_video_dev_unregister_backlight() during device removal.
If the work executes after acpi_video_bus_unregister_backlight() frees these resources, it causes a use-after-free when acpi_video_switch_brightness() dereferences device->brightness or device->backlight.
Fix this by calling cancel_delayed_work_sync() for each device's switch_brightness_work in acpi_video_bus_remove_notify_handler() after removing the notify handler that queues the work. This ensures the work completes before the memory is freed.
[ rjw: Changelog edit ]
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Analysis
by VulDB Data Team • 05/19/2026
The vulnerability described in CVE-2025-40211 represents a critical use-after-free condition within the Linux kernel's ACPI video subsystem, specifically affecting the acpi_video_switch_brightness() function. This flaw occurs during the dynamic removal of video devices from the system, where the kernel's ACPI video driver manages display brightness through a delayed work mechanism. The issue manifests when the system attempts to switch video brightness while a device is being removed, creating a race condition between the work queue execution and resource deallocation processes. The vulnerability directly impacts the kernel's ability to safely manage hardware resources during device lifecycle operations, potentially leading to system instability or arbitrary code execution.
The technical root cause of this vulnerability stems from improper synchronization between the delayed work execution and the device removal process in the ACPI video subsystem. When acpi_video_bus_remove_notify_handler() is invoked during device removal, it queues switch_brightness_work to handle brightness switching operations, but fails to ensure this work completes before the device resources are freed. The device structure contains pointers to brightness and backlight information that get deallocated by acpi_video_dev_unregister_backlight() during the removal sequence, while switch_brightness_work may still attempt to access these freed memory locations. This classic use-after-free scenario occurs because the kernel's work queue mechanism does not guarantee that all pending work items will complete before resource deallocation, creating a window where memory access violations can occur.
The operational impact of this vulnerability extends beyond simple system crashes, potentially enabling privilege escalation and system compromise within the kernel space. Attackers could exploit this condition by triggering device removal operations while brightness switching work is pending, causing the kernel to access freed memory locations and potentially execute arbitrary code with kernel privileges. The vulnerability affects systems running Linux kernels that implement the ACPI video subsystem, particularly those managing display hardware through ACPI interfaces, making it relevant to laptops, desktops, and servers with integrated graphics. The risk is elevated in environments where dynamic device management occurs frequently, such as during system updates, hot-plug operations, or automated device management scenarios.
The fix implemented for CVE-2025-40211 addresses the synchronization issue by introducing proper work queue cancellation before resource deallocation. The solution involves calling cancel_delayed_work_sync() for each device's switch_brightness_work within acpi_video_bus_remove_notify_handler() immediately after removing the notify handler that queues the work. This ensures that all pending brightness switching operations complete before the device resources are freed, eliminating the race condition that previously allowed access to freed memory. This approach aligns with established security practices for kernel memory management and follows the principle of proper resource cleanup ordering. The fix specifically addresses the CWE-416 vulnerability category, which covers use-after-free conditions, and demonstrates effective application of the ATT&CK technique T1068 for privilege escalation through kernel exploitation. The solution maintains system stability while preserving the intended functionality of the ACPI video subsystem's brightness management capabilities.