Improper input validation in Linux kernel - CVE-2026-63853

Vulnerability identifier: #VU138794

CSH Severity: Low

CVSS v4: 6.8 [CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-63853

CWE-ID: CWE-20

Exploitation vector: Local access

Exploit availability: No public exploit available

The vulnerability allows a local user to cause a denial of service.

The vulnerability exists due to improper input validation in the VCN v4.0 encoder ring submission handling when processing command submissions with user fences. A local user can submit a crafted command stream with a user fence to cause a denial of service.

The issue affects VCN v4.0 encoder functionality, and stems from unsupported 64-bit user fence writes being accepted.

Linux kernel
Ubuntu
linux-ibm (Ubuntu package)
linux-azure (Ubuntu package)
linux-aws (Ubuntu package)
linux-nvidia (Ubuntu package)
linux-nvidia-bos (Ubuntu package)

Install security update from vendor's repository.

Linux kernel - update to 7.0 rc3
linux-ibm (Ubuntu package) - addressed in versions 7.0.0-1008.8, 7.0.0-1010.10
linux-azure (Ubuntu package) - addressed in versions 7.0.0-1009.9, 7.0.0-1010.10
linux-aws (Ubuntu package) - addressed in versions 7.0.0-1009.9, 7.0.0-1015.15
linux-nvidia (Ubuntu package) - addressed in versions 7.0.0-1016.16, 7.0.0-1016.16~24.04.1
linux-nvidia-bos (Ubuntu package) - update to 7.0.0-2016.16

• https://git.kernel.org/stable/c/1286b6872de0aee1feeeaa6dbac86369806de9a5
• https://git.kernel.org/stable/c/51f694221047c84fa185be98210eb2c354ffb8c6
• https://git.kernel.org/stable/c/6bdd2ed6458d35c368fbe9550a4d7f342abd3a92

• Improper input validation in Linux kernel amd amdgpu driver
• Ubuntu update for linux-ibm
• Ubuntu update for linux-azure
• Ubuntu update for linux-aws
• Ubuntu update for linux-nvidia-bos
• Ubuntu update for linux-nvidia