CVE-2026-31527: Linux Kernel Use-After-Free Vulnerability

CVE-2026-31527 Overview

A Use-After-Free (UAF) vulnerability has been identified in the Linux kernel's platform driver core subsystem. The vulnerability exists in the driver attach mechanism where the driver_override field is accessed without proper locking during the bus' match() callback execution. When a driver is probed through __driver_attach(), the callback is invoked without holding the device lock, creating a race condition that can lead to memory corruption.

Critical Impact

This vulnerability allows potential exploitation through race conditions in the kernel's driver core, potentially enabling local privilege escalation or denial of service on affected Linux systems.

Affected Products

• Linux Kernel (multiple versions)

Discovery Timeline

• 2026-04-22 - CVE CVE-2026-31527 published to NVD
• 2026-04-23 - Last updated in NVD database

Technical Details for CVE-2026-31527

Vulnerability Analysis

The vulnerability resides in the Linux kernel's platform driver core infrastructure, specifically in how the driver_override field is handled during driver-device matching operations. The __driver_attach() function initiates the driver probing process by calling the bus' match() callback. However, this callback is executed without acquiring the device lock, which is an intentional design decision for performance reasons.

The driver_override mechanism allows administrators to force a specific driver to bind to a device, bypassing the normal driver selection process. When this field is accessed concurrently without synchronization—one thread reading during match() while another thread modifies or frees the override string—a Use-After-Free condition occurs. This can result in the kernel dereferencing freed memory, leading to potential information disclosure, denial of service, or arbitrary code execution in kernel context.

Root Cause

The root cause is improper synchronization when accessing the driver_override field in the platform driver subsystem. The existing implementation directly accessed this field without holding the appropriate device lock, while other code paths could simultaneously free or modify the memory. The fix transitions the platform driver code to use the generic driver-core driver_override infrastructure, which implements proper internal locking to serialize access to the override field.

Attack Vector

An attacker with local access to the system could potentially exploit this vulnerability by triggering concurrent operations on the driver_override sysfs interface while driver binding operations are in progress. The attack requires precise timing to win the race condition, but successful exploitation could allow:

1. Memory corruption - Writing to or reading from freed memory regions
2. Privilege escalation - Corrupting kernel memory structures to gain elevated privileges
3. Denial of service - Causing kernel panics or system instability

The vulnerability is exploitable locally and requires the attacker to have sufficient permissions to interact with the driver sysfs interfaces.

Detection Methods for CVE-2026-31527

Indicators of Compromise

• Unexpected kernel panics or oops messages referencing __driver_attach, platform_match, or driver_override functions
• Kernel log entries showing memory corruption or invalid memory access in driver core subsystems
• System instability during device driver loading or unloading operations

Detection Strategies

• Monitor kernel logs (dmesg) for UAF-related warnings or KASAN (Kernel Address Sanitizer) reports in driver core functions
• Deploy kernel instrumentation to detect anomalous access patterns to driver_override sysfs entries
• Use Linux Security Modules (LSM) to audit access to /sys/bus/platform/devices/*/driver_override paths

Monitoring Recommendations

• Enable KASAN in development/testing kernels to proactively detect memory safety violations
• Configure audit rules to log modifications to driver_override sysfs entries on production systems
• Monitor for unusual patterns of driver binding/unbinding operations that could indicate exploitation attempts

How to Mitigate CVE-2026-31527

Immediate Actions Required

• Update to a patched Linux kernel version that includes the driver-core driver_override infrastructure fix
• Review and restrict access to sysfs driver_override interfaces using appropriate file permissions or SELinux/AppArmor policies
• Prioritize patching on systems where untrusted local users have access

Patch Information

The Linux kernel maintainers have released patches that transition the platform driver code to use the generic driver-core driver_override infrastructure, which handles proper locking internally. The fix ensures that access to the driver_override field is properly serialized, eliminating the race condition.

Multiple kernel commits address this vulnerability across different kernel versions:

• Linux Kernel Commit 2b38efc05bf7
• Linux Kernel Commit 7c02a9bd7d14
• Linux Kernel Commit 9a6086d2a828
• Linux Kernel Commit edee7ee5a14c

Workarounds

• Restrict write access to /sys/bus/platform/devices/*/driver_override to root only
• Use SELinux or AppArmor to limit which processes can access driver_override sysfs entries
• Consider disabling driver_override functionality if not required for system operation

# Restrict driver_override access permissions
chmod 600 /sys/bus/platform/devices/*/driver_override

# SELinux example to restrict access (add to local policy)
# audit allow domain driver_override_t:file { read write };