CVE-2025-71315: Linux Kernel DRM VKMS Vulnerability

CVE-2025-71315 Overview

CVE-2025-71315 affects the Linux kernel Virtual Kernel Mode Setting (VKMS) Direct Rendering Manager (DRM) driver. The issue involves the vblank timer handling in drm/vkms, which the upstream maintainers resolved by replacing the custom vkms vblank timer with the standard DRM implementation. The fix removes the bespoke hrtimer from struct vkms_output and routes vblank handling through DRM's vblank helpers and initializer macros. VKMS custom timeout logic is now invoked via handle_vblank_timeout in struct drm_crtc_helper_funcs. The change consolidates timer logic into the shared DRM subsystem to reduce duplicated handling paths.

Critical Impact
A flaw in the vkms vblank timer handling in the Linux kernel DRM subsystem was resolved by migrating to the standard DRM vblank timer implementation.

Affected Products

Linux kernel (mainline) with the drm/vkms driver enabled
Linux kernel stable branches receiving the backported fix
Distributions shipping kernels prior to the corresponding stable commit

Discovery Timeline

2026-06-08 - CVE-2025-71315 published to the National Vulnerability Database (NVD)
2026-06-08 - Last updated in NVD database

Technical Details for CVE-2025-71315

Vulnerability Analysis

The defect resides in the Virtual Kernel Mode Setting (VKMS) driver located under drivers/gpu/drm/vkms in the Linux kernel tree. VKMS is a software-only DRM driver primarily used for testing the DRM subsystem and running graphical workloads without physical display hardware. Prior to the fix, vkms implemented its own vblank timer using a high-resolution timer (hrtimer) stored in struct vkms_output. This implementation duplicated logic that the shared DRM core already provides through its vblank helpers.

The Common Vulnerabilities and Exposures (CVE) entry does not classify a specific Common Weakness Enumeration (CWE) category, and no exploitation vector has been publicly documented. The upstream change converts vkms to the standard DRM vblank timer, removing the custom hrtimer and wiring the existing vkms timeout routine into handle_vblank_timeout within struct drm_crtc_helper_funcs.

Root Cause

The root cause is divergence between the custom vkms vblank timer and the DRM core's vblank timer helper. Although conceptually identical, the two implementations differed at the code level, which created maintenance burden and potential for inconsistent timer state handling within the DRM subsystem.

Attack Vector

The public CVE record does not specify an attack vector, exploitability assessment, or Common Vulnerability Scoring System (CVSS) vector. VKMS is typically loaded in test environments or virtualized graphics stacks. No public proof-of-concept exists, and the issue is not listed in the Cybersecurity and Infrastructure Security Agency (CISA) Known Exploited Vulnerabilities catalog.

No verified exploitation code is available. Refer to the upstream commits for the technical fix details:

Detection Methods for CVE-2025-71315

Indicators of Compromise

No public indicators of compromise are associated with CVE-2025-71315.
The Exploit Prediction Scoring System (EPSS) probability is 0.018% (5.19 percentile), indicating very low predicted exploitation activity.

Detection Strategies

Inventory kernel versions across Linux hosts and compare against the patched stable branches referenced in the upstream commits.
Identify systems where the vkms kernel module is loaded by querying lsmod | grep vkms or auditing module load events.
Track kernel package versions through configuration management tools to identify unpatched assets.

Monitoring Recommendations

Monitor kernel module load events for vkms on production hosts where it is not expected.
Subscribe to distribution security advisories for kernel updates referencing the drm/vkms subsystem.
Review kernel logs (dmesg) for unexpected DRM or vblank timer warnings.

How to Mitigate CVE-2025-71315

Immediate Actions Required

Apply the kernel update from your Linux distribution that incorporates the upstream drm/vkms vblank timer conversion.
Verify the vkms module is only loaded on systems where it is required, such as graphics testing environments.
Track upstream stable kernel releases for the backport status of the referenced commits.

Patch Information

The upstream resolution converts vkms to use the DRM vblank timer helpers. The relevant commits are 02e2681ffe1a and a0582cc92398. Consult your distribution's kernel changelog to confirm inclusion.

Workarounds

Unload the vkms module on systems that do not require it using modprobe -r vkms.
Blacklist the vkms module on production servers where virtual display functionality is not needed.
Restrict module loading privileges to root and limit local access on systems where the module remains enabled.

bash

# Blacklist the vkms module to prevent loading
echo "blacklist vkms" | sudo tee /etc/modprobe.d/blacklist-vkms.conf
sudo update-initramfs -u

# Verify the module is not currently loaded
lsmod | grep vkms