CVE-2026-45834: Linux Kernel Bluetooth L2CAP Vulnerability

CVE-2026-45834 Overview

CVE-2026-45834 is a null pointer dereference vulnerability in the Linux kernel Bluetooth Logical Link Control and Adaptation Protocol (L2CAP) subsystem. The flaw resides in the l2cap_sock_state_change_cb() callback, which did not include the NULL guard already present in the related l2cap_sock_resume_cb() and l2cap_sock_ready_cb() functions. When the callback executed against a socket without a valid associated structure, the kernel could dereference a NULL pointer and crash. The upstream fix adds the missing NULL check to align state-change handling with the other callbacks.

Critical Impact
Triggering the unguarded callback path can cause a kernel-mode NULL pointer dereference, leading to a denial-of-service condition on affected Linux systems with Bluetooth enabled.

Affected Products

Linux kernel (mainline) prior to the commits referenced in the upstream fix
Linux kernel stable branches receiving the backported fixes (1810e42, 2ff1a41, 5105f3e, a2dcf1a, c88c185)
Distributions shipping affected kernel versions with Bluetooth L2CAP support enabled

Discovery Timeline

2026-05-26 - CVE-2026-45834 published to NVD
2026-05-26 - Last updated in NVD database

Technical Details for CVE-2026-45834

Vulnerability Analysis

The Linux kernel Bluetooth stack uses L2CAP to provide connection-oriented and connectionless data services over Bluetooth. L2CAP sockets register a set of callbacks invoked during state transitions, including l2cap_sock_state_change_cb(), l2cap_sock_resume_cb(), and l2cap_sock_ready_cb(). The latter two functions already validated that the socket pointer was non-NULL before dereferencing it, but l2cap_sock_state_change_cb() omitted that defensive check. Under timing conditions where the callback fired without a fully initialized socket context, the kernel dereferenced a NULL pointer and produced an oops.

Root Cause

The root cause is a missing NULL pointer guard [CWE-476] in l2cap_sock_state_change_cb(). The patch resolves the inconsistency by adding the same NULL check used by sibling callbacks, ensuring the function returns safely when no socket is associated with the state change event.

Attack Vector

The NVD entry does not publish a CVSS vector or confirmed attack scenario. L2CAP callbacks are exercised through Bluetooth connection state transitions, so any path that drives a state change against a socket lacking the expected context can reach the vulnerable code. Exploitation requires conditions under which the callback runs without a valid socket pointer, producing a kernel crash rather than code execution. No public proof-of-concept or exploit is listed in the available references.

No verified exploitation code is available. Refer to the upstream commits listed in the references for the exact source-level changes.

Detection Methods for CVE-2026-45834

Indicators of Compromise

Kernel oops messages referencing l2cap_sock_state_change_cb in dmesg, /var/log/kern.log, or the systemd journal
Unexpected reboots or Bluetooth subsystem failures on hosts with bluetoothd running
Crash dumps showing a NULL pointer dereference in the net/bluetooth/l2cap_sock.c call path

Detection Strategies

Inventory running kernel versions across Linux endpoints and servers and compare against the fixed commit hashes (1810e42, 2ff1a41, 5105f3e, a2dcf1a, c88c185)
Monitor kernel ring buffers for repeated Bluetooth-related oops or panic signatures, which can indicate either bug triggers or DoS attempts
Correlate Bluetooth connection events with subsequent kernel instability on hosts that expose Bluetooth to untrusted devices

Monitoring Recommendations

Forward kernel and bluetoothd logs to a centralized logging or SIEM platform for retrospective analysis
Alert on kernel BUG or Oops strings in syslog streams from endpoints that are not expected to crash
Track patch deployment status across Linux fleets and flag systems still running pre-fix kernels

How to Mitigate CVE-2026-45834

Immediate Actions Required

Update affected Linux kernels to a version containing the upstream fix commits referenced by the maintainers
Where patching is not immediately feasible, disable the Bluetooth stack on systems that do not require it using rmmod bluetooth or by blacklisting the module
Restrict physical and radio proximity access for hosts where Bluetooth must remain enabled

Patch Information

The fix is published in the upstream Linux kernel via the following commits: Kernel Git Commit 1810e42, Kernel Git Commit 2ff1a41, Kernel Git Commit 5105f3e, Kernel Git Commit a2dcf1a, and Kernel Git Commit c88c185. Each commit adds the NULL guard to l2cap_sock_state_change_cb() on the relevant stable branch.

Workarounds

Unload the Bluetooth modules on systems that do not need them: modprobe -r bnep rfcomm bluetooth
Add a blacklist bluetooth entry under /etc/modprobe.d/ to prevent automatic loading at boot
Stop and mask the bluetooth.service unit on servers and appliances that do not require wireless connectivity

bash

# Configuration example
# Disable and mask the Bluetooth service
sudo systemctl stop bluetooth.service
sudo systemctl disable bluetooth.service
sudo systemctl mask bluetooth.service

# Prevent the kernel modules from loading
echo "blacklist bluetooth" | sudo tee /etc/modprobe.d/disable-bluetooth.conf
echo "blacklist btusb" | sudo tee -a /etc/modprobe.d/disable-bluetooth.conf
sudo update-initramfs -u