CVE-2026-23462: Linux Kernel Use-After-Free Vulnerability

CVE-2026-23462 Overview

CVE-2026-23462 is a Use-After-Free (UAF) vulnerability in the Linux kernel's Bluetooth HIDP (Human Interface Device Profile) subsystem. The vulnerability occurs when the l2cap_conn reference is not properly dropped during the user->remove callback invocation, leading to potential memory corruption and system instability.

The issue manifests in the L2CAP (Logical Link Control and Adaptation Protocol) connection handling code within the Bluetooth stack. When a Bluetooth HID connection is terminated, the kernel fails to correctly manage reference counts for the l2cap_conn structure, resulting in a use-after-free condition that can be triggered during device unregistration or connection teardown.

Critical Impact

This vulnerability can lead to kernel memory corruption, system crashes, or potential privilege escalation through exploitation of the UAF condition in the Bluetooth subsystem.

Affected Products

• Linux Kernel (versions with vulnerable Bluetooth HIDP implementation)
• Systems with Bluetooth HID device support enabled
• Linux-based distributions with affected kernel versions

Discovery Timeline

• 2026-04-03 - CVE CVE-2026-23462 published to NVD
• 2026-04-07 - Last updated in NVD database

Technical Details for CVE-2026-23462

Vulnerability Analysis

This Use-After-Free vulnerability exists in the Linux kernel's Bluetooth HIDP subsystem, specifically in the L2CAP connection management code. The root issue is a reference counting error where the l2cap_conn reference is not properly released when the user->remove callback is invoked during connection cleanup.

The stack trace from the vulnerability shows the execution path through several key kernel functions:

• l2cap_conn_free() - The function responsible for freeing the L2CAP connection structure
• l2cap_conn_del() - Connection deletion handler that manages reference counting via kref
• l2cap_disconn_cfm() - Disconnection confirmation callback
• hci_conn_hash_flush() - Flushes all connections during HCI device unregistration
• hci_dev_close_sync() - Synchronously closes the HCI device
• hci_unregister_dev() - Unregisters the Bluetooth HCI device
• vhci_release() - Release handler for the virtual HCI driver

The vulnerability can be triggered when a Bluetooth HID device connection is terminated, particularly during device unregistration or when the virtual HCI device file is closed. The premature freeing of the l2cap_conn structure while references still exist creates a classic UAF scenario.

Root Cause

The root cause is improper reference count management in the Bluetooth L2CAP layer. When the user->remove callback is called during connection teardown, the code fails to drop the l2cap_conn reference appropriately. This reference counting imbalance causes the connection structure to be freed while other parts of the kernel still hold references to it.

The issue is located in the interaction between net/bluetooth/l2cap_core.c and the HIDP layer. The l2cap_conn_free() function at line 1808 of l2cap_core.c is invoked while the connection object is still being accessed elsewhere in the kernel.

Attack Vector

The attack vector involves manipulating Bluetooth HID device connections to trigger the vulnerable code path. An attacker with local access could:

1. Establish a Bluetooth HIDP connection (either through a real device or using the virtual HCI interface)
2. Trigger a connection termination scenario that exercises the vulnerable user->remove callback path
3. Race to access the freed l2cap_conn structure before it is reallocated
4. Potentially achieve code execution or privilege escalation through controlled memory corruption

The vulnerability requires local access to a system with Bluetooth capabilities and the ability to create or manipulate Bluetooth HID connections. The virtual HCI driver (hci_vhci.c) provides a convenient interface for triggering this vulnerability without requiring physical Bluetooth hardware.

Detection Methods for CVE-2026-23462

Indicators of Compromise

• Kernel panic or oops messages referencing l2cap_conn_free or l2cap_conn_del functions
• Unexpected system crashes during Bluetooth device disconnection events
• KASAN (Kernel Address Sanitizer) reports indicating use-after-free in net/bluetooth/l2cap_core.c
• Abnormal Bluetooth subsystem behavior following HID device disconnections

Detection Strategies

• Enable kernel memory debugging features (KASAN, KFENCE) to detect UAF conditions
• Monitor kernel logs for stack traces involving l2cap_conn_free and related Bluetooth functions
• Deploy runtime integrity monitoring for kernel memory structures
• Use SentinelOne's kernel-level threat detection to identify exploitation attempts

Monitoring Recommendations

• Configure syslog monitoring for kernel Bluetooth subsystem errors and warnings
• Enable audit logging for Bluetooth device registration/unregistration events
• Monitor for unusual /dev/vhci file operations that could indicate exploitation attempts
• Implement alerting on kernel panic events related to Bluetooth stack functions

How to Mitigate CVE-2026-23462

Immediate Actions Required

• Apply the kernel patches from the official Linux kernel Git repository
• Consider disabling Bluetooth functionality on critical systems until patched
• Restrict access to the virtual HCI interface (/dev/vhci) to trusted users only
• Update to a patched kernel version as soon as available from your distribution

Patch Information

Multiple patches have been committed to the Linux kernel stable tree to address this vulnerability. The fix ensures proper reference count management for l2cap_conn structures during the user->remove callback execution.

Available patch commits:

• Kernel Git Commit 21a47a1
• Kernel Git Commit 45ebe5b
• Kernel Git Commit 4d37fa7
• Kernel Git Commit 7c805b7
• Kernel Git Commit dbf666e
• Kernel Git Commit f8b6ed2

Workarounds

• Disable Bluetooth at the kernel level by blacklisting the bluetooth module: echo "blacklist bluetooth" >> /etc/modprobe.d/bluetooth-disable.conf
• Remove or restrict permissions on /dev/vhci to prevent virtual HCI exploitation
• Use kernel boot parameters to disable Bluetooth: add btusb.disable_autosuspend=1 or disable Bluetooth modules entirely
• Implement network segmentation to limit Bluetooth attack surface in enterprise environments

# Configuration example
# Disable Bluetooth kernel module to mitigate CVE-2026-23462
echo "blacklist bluetooth" >> /etc/modprobe.d/bluetooth-disable.conf
echo "blacklist btusb" >> /etc/modprobe.d/bluetooth-disable.conf
echo "blacklist hci_vhci" >> /etc/modprobe.d/bluetooth-disable.conf

# Restrict virtual HCI device access
chmod 600 /dev/vhci 2>/dev/null || true

# Reload module configuration
update-initramfs -u