CVE-2026-31582: Linux Kernel Use-After-Free Vulnerability

CVE-2026-31582 Overview

A use-after-free vulnerability has been identified in the Linux kernel's hardware monitoring (hwmon) subsystem, specifically within the powerz driver. This vulnerability occurs during USB device disconnection when powerz_disconnect() frees the URB (USB Request Block) and releases the mutex, allowing a subsequent powerz_read() call to acquire the mutex and invoke powerz_read_data(), which then dereferences the already-freed URB pointer.

Critical Impact
Local attackers with low privileges can exploit this use-after-free condition to potentially achieve arbitrary code execution, escalate privileges, or cause system instability through kernel memory corruption.

Affected Products

Linux Kernel (multiple versions with powerz hwmon driver)

Discovery Timeline

2026-04-24 - CVE-2026-31582 published to NVD
2026-04-27 - Last updated in NVD database

Technical Details for CVE-2026-31582

Vulnerability Analysis

This vulnerability is classified as a Use-After-Free (CWE-416) condition in the Linux kernel's powerz hardware monitoring driver. The flaw stems from a race condition between the USB disconnect handler and concurrent read operations on the device.

When a USB device is physically disconnected or programmatically removed, the powerz_disconnect() function executes and frees the URB structure. However, the driver's synchronization mechanism was insufficient—after the URB was freed and the mutex released, another thread could acquire the same mutex and proceed to call powerz_read_data(). This function would then attempt to dereference the URB pointer, which now points to freed memory.

Exploitation of this vulnerability requires local access to the system and the ability to interact with the powerz hardware monitoring interface. An attacker could potentially trigger the race condition by timing USB disconnect events with read operations, leading to kernel memory corruption that could be leveraged for privilege escalation or arbitrary code execution within the kernel context.

Root Cause

The root cause is improper synchronization between the USB disconnect handler and the device read path. Specifically, the driver failed to properly signal to concurrent readers that the device had been disconnected and its resources freed. The original code path allowed powerz_read_data() to proceed with a stale URB pointer after powerz_disconnect() had already freed the memory.

Attack Vector

This vulnerability requires local access to the system. An attacker with low-level privileges can exploit the race condition by:

Initiating read operations on the powerz hwmon interface
Triggering a USB disconnect event (either physically or through software means)
Timing the operations to cause powerz_read_data() to execute after the URB has been freed but before the read operation completes

The kernel fix addresses this by setting priv->urb to NULL in powerz_disconnect() after freeing, adding a null check at the start of powerz_read_data() to return -ENODEV for disconnected devices, and reordering usb_set_intfdata() before hwmon registration to ensure the disconnect handler can always locate the private data structure.

Detection Methods for CVE-2026-31582

Indicators of Compromise

Kernel crash logs or oops messages referencing the powerz hwmon driver or USB subsystem
System instability or unexpected reboots following USB device disconnection events
Memory corruption errors in kernel logs associated with hwmon or USB operations
Suspicious local user activity involving repeated USB device manipulation

Detection Strategies

Monitor kernel logs (dmesg) for use-after-free warnings or KASAN (Kernel Address Sanitizer) reports related to powerz driver
Implement kernel tracing on the powerz driver functions to detect anomalous call patterns during USB events
Deploy runtime memory safety tools like KASAN in development or staging environments to catch exploitation attempts

Monitoring Recommendations

Enable kernel auditing for USB device connect/disconnect events on systems with powerz-compatible hardware
Monitor for unusual patterns of USB device enumeration and removal
Configure alerting on kernel panic or oops conditions, particularly those mentioning hwmon or USB drivers

How to Mitigate CVE-2026-31582

Immediate Actions Required

Update the Linux kernel to a patched version containing the fix commits
On systems where immediate patching is not possible, consider unloading the powerz hwmon kernel module if the hardware is not critical
Restrict local access to untrusted users on affected systems until patching is complete

Patch Information

The Linux kernel maintainers have released fixes across multiple stable branches. The patches address the vulnerability by properly nullifying the URB pointer during disconnect and adding defensive checks in the read path. The following commits contain the fix:

Workarounds

Unload the powerz kernel module if the hardware monitoring functionality is not required: modprobe -r powerz
Blacklist the powerz module to prevent automatic loading by adding blacklist powerz to /etc/modprobe.d/blacklist.conf
Restrict physical access to USB ports on affected systems to prevent malicious device manipulation

bash

# Temporarily unload the powerz module
modprobe -r powerz

# Permanently blacklist the powerz module
echo "blacklist powerz" | sudo tee /etc/modprobe.d/powerz-blacklist.conf

# Verify the module is not loaded
lsmod | grep powerz