CVE-2026-23291: Linux Kernel Use-After-Free Vulnerability

CVE-2026-23291 Overview

A vulnerability has been identified in the Linux kernel's NFC pn533 driver that improperly handles USB interface reference counting during device disconnection. When the device is disconnected from the driver, a dangling reference count remains on the USB interface that was acquired during the probe callback, leading to improper resource management.

Critical Impact

This vulnerability can lead to resource leaks and potential system instability due to improper reference count handling in the Linux kernel's NFC subsystem.

Affected Products

• Linux kernel with NFC pn533 driver enabled
• Systems using PN533-based NFC USB devices
• Linux kernel versions prior to the security patches

Discovery Timeline

• 2026-03-25 - CVE CVE-2026-23291 published to NVD
• 2026-03-25 - Last updated in NVD database

Technical Details for CVE-2026-23291

Vulnerability Analysis

This vulnerability resides in the NFC pn533 driver within the Linux kernel. The driver is responsible for managing PN533-based NFC (Near Field Communication) USB devices. During the normal device lifecycle, the probe callback acquires a reference count on the USB interface to ensure the interface remains valid while the driver is using it.

The issue occurs during the disconnect phase when the device is removed or disconnected from the system. The driver fails to properly drop the USB interface reference that was grabbed during the probe callback, resulting in a "dangling" reference count. This improper reference counting can lead to resource leaks and potentially prevent the USB interface from being properly cleaned up.

Reference counting is a critical mechanism in the Linux kernel for managing the lifecycle of objects and ensuring resources are freed only when no longer in use. When reference counts are not properly managed, it can lead to memory leaks, use-after-free conditions, or prevent proper resource cleanup.

Root Cause

The root cause of this vulnerability is the missing call to properly release the USB interface reference in the disconnect handler of the pn533 driver. During probe, the driver increments the reference count on the USB interface, but the corresponding decrement is missing in the disconnect path. This creates a reference leak where the USB interface object maintains a higher reference count than expected, preventing proper cleanup.

Attack Vector

This vulnerability is classified with an unknown attack vector. It is primarily a resource management issue that manifests during device disconnection events. While exploitation requires local access or physical interaction with NFC USB devices, the vulnerability could potentially be triggered through:

• Physical disconnection of PN533-based NFC USB devices
• Software-initiated USB device removal or unbinding
• Hot-plugging scenarios involving NFC hardware

The vulnerability does not appear to have remote exploitation capabilities, as it requires interaction with the local USB subsystem.

Detection Methods for CVE-2026-23291

Indicators of Compromise

• Unexpected resource exhaustion related to USB interface objects
• Kernel warnings or errors related to USB reference counting in system logs
• Memory leaks observed in kernel memory usage over time with NFC device operations

Detection Strategies

• Monitor kernel logs (dmesg) for warnings related to pn533 driver or USB reference counting issues
• Track USB subsystem behavior during NFC device connect/disconnect cycles
• Use kernel memory debugging tools like kmemleak to identify reference count leaks

Monitoring Recommendations

• Enable kernel debugging options to track reference counting anomalies
• Implement system monitoring for unusual memory growth patterns in USB subsystems
• Review /sys/kernel/debug/usb/ for USB device state inconsistencies

How to Mitigate CVE-2026-23291

Immediate Actions Required

• Apply the latest Linux kernel security patches that address this vulnerability
• Update to a patched kernel version that includes the reference counting fix
• If immediate patching is not possible, consider disabling the pn533 driver module if NFC functionality is not required

Patch Information

Multiple patches have been released to address this vulnerability in the Linux kernel stable branches. The fix ensures that the USB interface reference is properly dropped in the disconnect callback after the driver is done using it.

Relevant kernel commits:

• Kernel Git Commit 00477cab
• Kernel Git Commit 12133a48
• Kernel Git Commit 4551d6ce
• Kernel Git Commit 7398d657
• Kernel Git Commit 7ff14eb0
• Kernel Git Commit d1f6d20b

Workarounds

• Disable the pn533 kernel module if NFC functionality is not required: modprobe -r pn533
• Blacklist the pn533 module to prevent automatic loading: add blacklist pn533 to /etc/modprobe.d/blacklist.conf
• Limit physical access to USB ports to reduce the risk of NFC device manipulation

# Disable pn533 module temporarily
modprobe -r pn533

# Blacklist the module permanently (add to /etc/modprobe.d/blacklist.conf)
echo "blacklist pn533" >> /etc/modprobe.d/blacklist.conf

# Verify module is not loaded
lsmod | grep pn533