CVE-2026-23149: Linux Kernel Privilege Escalation Flaw

CVE-2026-23149 Overview

A vulnerability has been identified in the Linux kernel's Direct Rendering Manager (DRM) subsystem, specifically within the drm_gem_change_handle_ioctl() function. The flaw allows unprivileged userspace applications to trigger kernel warnings by passing GEM buffer object handles larger than INT_MAX. This occurs due to a type mismatch between the userspace API (which uses u32 for handles) and the internal implementation that relies on idr_alloc() (which operates on signed int ranges).

Critical Impact

Unprivileged local users can trigger kernel warnings, potentially leading to system instability or denial of service conditions through repeated exploitation of the integer boundary condition.

Affected Products

• Linux kernel with DRM subsystem enabled
• Systems using GEM (Graphics Execution Manager) for buffer object management
• Graphics drivers utilizing DRM GEM handle operations

Discovery Timeline

• 2026-02-14 - CVE CVE-2026-23149 published to NVD
• 2026-02-18 - Last updated in NVD database

Technical Details for CVE-2026-23149

Vulnerability Analysis

The vulnerability stems from an improper input validation issue in the DRM GEM handle management code. The Graphics Execution Manager (GEM) subsystem uses handles to reference buffer objects allocated by the kernel for graphics operations. These handles are defined as u32 (unsigned 32-bit integers) in the userspace API, allowing values from 0 to 4,294,967,295.

However, the kernel's internal implementation uses idr_alloc() for handle allocation, which operates on signed integer ranges. When a userspace application passes a handle value larger than INT_MAX (2,147,483,647), the conversion from u32 to int causes the value to become negative, triggering the WARN_ON_ONCE(start < 0) check in idr_alloc().

Root Cause

The root cause is a boundary condition error where the drm_gem_change_handle_ioctl() function fails to validate that the incoming u32 handle value from userspace falls within the valid range for the idr_alloc() internal implementation. The fix introduces explicit rejection of handle values above INT_MAX and improves the clarity of end limit calculations by performing them in the signed integer domain.

Attack Vector

An attacker with local access can exploit this vulnerability by making IOCTL calls to the DRM subsystem with crafted GEM handle values exceeding INT_MAX. The attack requires:

1. Access to a DRM device node (typically /dev/dri/*)
2. Ability to invoke the drm_gem_change_handle_ioctl() function
3. Passing a malicious handle value in the range INT_MAX + 1 to UINT32_MAX

The vulnerability is triggered when idr_alloc() receives a negative start value due to the signed/unsigned integer conversion, causing the kernel to emit a warning. While this does not directly allow code execution, repeated triggering could impact system stability or be used as part of a larger attack chain.

Technical details and the actual patch implementation can be found in the kernel git commit 12f15d5 and kernel git commit ae8831e.

Detection Methods for CVE-2026-23149

Indicators of Compromise

• Kernel log messages containing WARN_ON_ONCE from idr_alloc() function
• Unusual patterns of DRM IOCTL calls with large handle values
• Repeated kernel warnings originating from the DRM subsystem
• System logs showing warnings from drm_gem_change_handle_ioctl()

Detection Strategies

• Monitor kernel logs (dmesg or /var/log/kern.log) for DRM-related warnings
• Implement syscall auditing for DRM IOCTL operations with anomalous parameters
• Deploy SentinelOne Singularity Platform for real-time kernel-level threat detection
• Use kernel tracing tools (ftrace, eBPF) to monitor drm_gem_change_handle_ioctl() invocations

Monitoring Recommendations

• Enable kernel warning monitoring through syslog or journald with alerting on DRM subsystem events
• Configure rate limiting on DRM device access for non-privileged users
• Implement SentinelOne agents on Linux systems to detect exploitation attempts through behavioral analysis

How to Mitigate CVE-2026-23149

Immediate Actions Required

• Update the Linux kernel to a patched version containing the fix
• Review and restrict access to DRM device nodes (/dev/dri/*) where possible
• Monitor systems for signs of exploitation attempts
• Deploy SentinelOne Singularity XDR for comprehensive endpoint protection

Patch Information

The vulnerability has been addressed in the Linux kernel through commits that add explicit validation to reject handle values above INT_MAX. The fix ensures that userspace cannot trigger kernel warnings through invalid handle values.

Patches are available at:

• Kernel Git Commit 12f15d5
• Kernel Git Commit ae8831e

Workarounds

• Restrict access to DRM device nodes by modifying udev rules to limit permissions
• Use SELinux or AppArmor policies to control which processes can access DRM devices
• Apply kernel lockdown features to limit userspace interaction with sensitive kernel interfaces

# Configuration example - Restrict DRM device access via udev rule
# Create /etc/udev/rules.d/99-drm-restrict.rules
KERNEL=="dri/*", GROUP="video", MODE="0660"
# Reload udev rules
udevadm control --reload-rules && udevadm trigger