CVE-2026-23227: Linux Kernel Use-After-Free Vulnerability

CVE-2026-23227 Overview

A race condition vulnerability has been identified in the Linux kernel's Exynos Virtual Display (vidi) driver. The vulnerability exists in the drm/exynos subsystem where memory allocation and deallocation operations for vidi_context member variables are performed without proper lock protection, leading to potential use-after-free conditions in concurrent execution scenarios.

Critical Impact

Use-after-free vulnerability in the Linux kernel display driver could allow memory corruption through concurrent access to freed EDID data structures, potentially leading to system instability or privilege escalation.

Affected Products

• Linux kernel with Exynos Virtual Display (vidi) driver enabled
• Systems utilizing the drm/exynos display subsystem
• Devices running Samsung Exynos-based display configurations

Discovery Timeline

• 2026-02-18 - CVE CVE-2026-23227 published to NVD
• 2026-02-18 - Last updated in NVD database

Technical Details for CVE-2026-23227

Vulnerability Analysis

The Exynos Virtual Display driver (drm/exynos/exynos_drm_vidi.c) contains a race condition vulnerability stemming from insufficient synchronization when accessing vidi_context structure members involved in memory allocation and deallocation. Specifically, the ctx->raw_edid pointer can be accessed by multiple CPU threads simultaneously without mutual exclusion, creating a classic Time-of-Check Time-of-Use (TOCTOU) vulnerability.

When vidi_connection_ioctl() is called concurrently from different contexts while drm_mode_getconnector() operations are in progress, a dangerous race window opens. One thread may free the drm_edid structure via drm_edid_free(ctx->raw_edid) while another thread is actively using the same memory through drm_edid_dup() and subsequent kmemdup() calls.

Root Cause

The root cause is the absence of mutex lock protection around critical sections that manipulate the ctx->raw_edid pointer and associated memory. The driver's ctx->lock mutex exists but was not being used to protect these operations. Without synchronization primitives guarding the allocation, assignment, and deallocation of the EDID data structure, concurrent accesses from multiple CPU cores can interleave in unexpected ways, leading to use-after-free conditions.

Attack Vector

The vulnerability can be triggered through a multi-threaded race condition involving three concurrent operations:

1. CPU0 executes vidi_connection_ioctl() with connection=true, allocating a new drm_edid structure and assigning it to ctx->raw_edid
2. CPU2 concurrently calls drm_mode_getconnector(), which invokes vidi_get_modes() and attempts to duplicate the EDID via drm_edid_dup(ctx->raw_edid)
3. CPU1 simultaneously executes vidi_connection_ioctl() with connection=false, freeing the EDID structure via drm_edid_free(ctx->raw_edid)

When CPU1's free operation completes before CPU2's kmemdup() call reads from the supposedly valid drm_edid->edid pointer, a use-after-free occurs. The kmemdup() function then reads from deallocated memory, potentially causing memory corruption, information disclosure, or kernel crashes.

The attack scenario involves concurrent ioctl calls on the virtual display device, which could be triggered by:

• Local user with access to the display device node
• Applications performing display configuration changes
• Display manager services managing display connections

Detection Methods for CVE-2026-23227

Indicators of Compromise

• Kernel oops or panics originating from drm/exynos driver code paths
• KASAN (Kernel Address Sanitizer) reports indicating use-after-free in vidi_get_modes() or drm_edid_dup() functions
• Unexpected memory corruption errors in display-related kernel modules

Detection Strategies

• Enable KASAN during kernel compilation to detect use-after-free at runtime
• Monitor kernel logs for warnings or errors from the exynos_drm_vidi module
• Deploy kernel debugging tools to trace concurrent access patterns in DRM subsystem calls

Monitoring Recommendations

• Configure kernel crash dump analysis to capture and analyze any panics related to the Exynos display driver
• Implement system monitoring for unexpected display driver failures or restarts
• Review audit logs for unusual patterns of ioctl calls to display device nodes

How to Mitigate CVE-2026-23227

Immediate Actions Required

• Update to a patched Linux kernel version that includes the fix commits
• Disable the Exynos Virtual Display driver if not required for system operation
• Restrict access to display device nodes to trusted users only

Patch Information

The vulnerability has been addressed in the Linux kernel stable branches. The fix implements proper mutex locking using ctx->lock to protect all member variables of vidi_context that are involved in memory allocation and deallocation operations.

Relevant kernel commits:

• Kernel Git Commit 0cd2c155740d
• Kernel Git Commit 60b75407c172

Workarounds

• Blacklist the exynos_drm module if virtual display functionality is not required
• Implement access controls to restrict which processes can interact with display device ioctls
• Consider running critical systems with KASAN enabled to detect exploitation attempts

# Configuration example
# Blacklist Exynos DRM module if not needed
echo "blacklist exynos_drm" >> /etc/modprobe.d/blacklist-exynos.conf
echo "blacklist exynos_drm_vidi" >> /etc/modprobe.d/blacklist-exynos.conf

# Restrict device permissions (if device exists)
chmod 600 /dev/dri/card*

# Update kernel to patched version
apt update && apt upgrade linux-image-$(uname -r)
# Or for RHEL-based systems:
# yum update kernel