CVE-2025-21968 in Linux
Summary
by MITRE • 04/01/2025
In the Linux kernel, the following vulnerability has been resolved:
drm/amd/display: Fix slab-use-after-free on hdcp_work
[Why]
A slab-use-after-free is reported when HDCP is destroyed but the property_validate_dwork queue is still running.
[How]
Cancel the delayed work when destroying workqueue.
(cherry picked from commit 725a04ba5a95e89c89633d4322430cfbca7ce128)
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Analysis
by VulDB Data Team • 02/01/2026
The vulnerability CVE-2025-21968 represents a critical slab-use-after-free condition within the Linux kernel's AMD display driver subsystem, specifically affecting the digital rights management implementation. This flaw exists in the drm/amd/display component where HDCP (High-bandwidth Digital Content Protection) functionality is handled, creating a dangerous scenario where memory allocated from the kernel's slab allocator is accessed after being freed. The issue manifests when the HDCP work queue is destroyed while the property_validate_dwork delayed work item is still executing or scheduled, leading to potential memory corruption that could be exploited by malicious actors.
The technical root cause stems from improper work queue management during HDCP destruction operations. When the display driver attempts to clean up HDCP resources, the system fails to properly cancel the delayed work item that was queued for property validation. This creates a race condition where the kernel's memory management subsystem frees the work structure while another execution path attempts to access it, resulting in undefined behavior and potential privilege escalation. The vulnerability specifically impacts systems utilizing AMD graphics hardware with HDCP support, making it particularly relevant for enterprise environments and multimedia applications that require content protection.
The operational impact of this vulnerability extends beyond simple memory corruption, as it can lead to system instability, crashes, or more severe exploitation scenarios. Attackers could potentially leverage this use-after-free condition to execute arbitrary code with kernel privileges, bypassing security boundaries that protect sensitive system resources. The vulnerability's exploitation potential aligns with ATT&CK technique T1068 (Exploitation for Privilege Escalation) and CWE-416 (Use After Free), where the freed memory region becomes accessible to unauthorized processes. Systems running affected kernel versions are particularly vulnerable during display configuration changes or when HDCP is actively managed, creating a window of opportunity for exploitation.
Mitigation strategies should focus on applying the patched kernel version containing the fix that properly cancels the delayed work queue during HDCP destruction. The solution involves ensuring that all pending work items are flushed and cancelled before destroying the workqueue, preventing the race condition that leads to the use-after-free scenario. Organizations should prioritize kernel updates and implement robust monitoring for unauthorized display configuration changes that might trigger the vulnerable code path. Additionally, system administrators should consider implementing memory protection mechanisms and monitoring for unusual kernel memory access patterns that could indicate exploitation attempts. The fix aligns with security best practices outlined in the Linux kernel security documentation and represents a standard approach to preventing work queue-related memory corruption vulnerabilities.