CVE-2026-23338: 
Linux Kernel vulnerability analysis and mitigation

CVE-2026-23338 is an improper input validation vulnerability in the Linux kernel's AMD GPU userq (user queue) driver that allows a local unprivileged user to trigger kernel warning backtraces via the userq wait ioctl. The flaw was disclosed on March 25, 2026, and affects Linux kernel versions 6.16, 6.16.1 through 6.18.16, 6.19 through 6.19.6, and 7.0 release candidates rc1 through rc7. It carries a CVSS v3.1 base score of 5.5 (Medium) (Red Hat Advisory, Red Hat Bugzilla).

The root cause is classified as CWE-1284 (Improper Validation of Specified Quantity in Input). In the drm/amdgpu/userq subsystem, the userq wait ioctl does not adequately validate the num_fences parameter supplied by userspace; if the value is too small — either deliberately or because the required fence count grew between two successive ioctl calls — the kernel previously emitted WARN_ON backtraces. The fix removes these WARN_ON macros so that the kernel simply returns an errno to userspace without generating a warning backtrace, since the condition does not represent a kernel fault (Red Hat Bugzilla, Kernel Git).

A local user with low privileges can repeatedly invoke the userq wait ioctl with an undersized num_fences value, causing the kernel to flood its logs with warning backtraces. This results in high availability impact through kernel log flooding, which can degrade system performance and obscure legitimate kernel warnings in monitoring and debugging pipelines. There is no confidentiality or integrity impact, and the attack is confined to the local system without scope change (Red Hat Advisory).

No public proof-of-concept exploit code is known to exist, and there is no evidence of in-the-wild exploitation as of the time of disclosure. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog. The EPSS score is approximately 0.017%, reflecting very low probability of exploitation in the near term (Red Hat Advisory).

• Logs: Repeated kernel warning backtraces in /var/log/kern.log or dmesg output originating from the drm/amdgpu/userq subsystem, particularly WARN_ON entries associated with fence count mismatches in the userq wait ioctl.
• Process: Unusual or high-frequency invocations of AMD GPU-related ioctls by unprivileged local processes, potentially visible via strace or audit logs targeting ioctl syscalls on /dev/dri/ device nodes.

Update the Linux kernel to a fixed version: 6.18.17 or later, 6.19.7 or later, or the final 7.0 release. Patches are available from the Linux kernel stable Git repositories and Red Hat's Bugzilla. As an interim measure on unpatched systems, restrict local user access to AMD GPU device nodes (e.g., /dev/dri/) where operationally feasible, and monitor kernel logs for anomalous drm/amdgpu/userq warning output (Red Hat Bugzilla, Kernel Git).