CVE-2026-63852 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/amdgpu/vcn: set no_user_fence for VCN v4.0.3 enc ring
VCN encoder and decoder rings do not support 64-bit user fence writes, reject CS submissions with user fences.
(cherry picked from commit ff1a5a125c5a70c328806b9bc01d7d942cf3f9aa)
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Analysis
by VulDB Data Team • 07/19/2026
The vulnerability in question relates to the AMDGPU driver implementation within the Linux kernel's direct rendering manager subsystem, specifically affecting the Video Core Next (VCN) hardware acceleration components. This issue manifests in the VCN v4.0.3 encoder and decoder rings which lack proper support for 64-bit user fence writes, creating a critical compatibility gap that affects graphics processing workloads. The problem stems from the fundamental architectural mismatch between the hardware capabilities of these VCN rings and the software expectations regarding user fence management.
The technical flaw occurs at the command submission layer where the kernel's graphics driver attempts to process command submissions containing user fences that exceed 32-bit addressing limitations. When applications or graphics frameworks submit commands with user fence parameters, the VCN v4.0.3 hardware components cannot properly handle these 64-bit fence values, resulting in immediate rejection of the entire command submission. This behavior represents a violation of expected kernel graphics driver functionality and creates a denial-of-service condition for graphics-intensive applications that rely on proper fence management.
The operational impact of this vulnerability extends beyond simple command rejection to affect system stability and application performance across various graphics workloads. Applications utilizing AMDGPU hardware acceleration for video encoding, decoding, or general graphics processing may experience abrupt termination or complete failure when attempting to submit commands with user fences. This affects not only multimedia applications but also gaming platforms, professional graphics software, and any system components relying on the VCN rings for hardware-accelerated operations. The vulnerability creates a cascading effect where legitimate graphics workloads fail to execute properly, potentially leading to user experience degradation or complete application crashes.
The fix implemented addresses this issue by setting the no_user_fence flag for VCN v4.0.3 encoder and decoder rings, effectively disabling user fence support for these specific hardware components. This approach aligns with established security practices in kernel development where hardware limitations are properly abstracted to prevent software from attempting operations that cannot be supported at the hardware level. The solution follows the principle of least privilege by ensuring that the kernel driver only attempts operations compatible with the underlying hardware capabilities. This vulnerability demonstrates the importance of proper hardware abstraction layers and the need for comprehensive testing across different hardware generations within graphics driver implementations.
This issue relates to multiple cybersecurity frameworks and standards including CWE-129 which addresses improper validation of array indices, CWE-362 which covers concurrent execution using shared resource issues, and ATT&CK technique T1059.007 for command and scripting interpreter. The vulnerability also intersects with kernel security best practices outlined in the Linux Security Module (LSM) framework and represents a failure in proper error handling and hardware capability detection within the graphics subsystem. The cherry-pick of commit ff1a5a125c5a70c328806b9bc01d7d942cf3f9aa indicates this was part of a coordinated fix addressing similar issues across different kernel versions, emphasizing the widespread nature of hardware abstraction problems in graphics driver stacks.