CVE-2026-68391: Linux Kernel Use-After-Free Vulnerability

CVE-2026-68391 Overview

CVE-2026-68391 is a use-after-free (UAF) vulnerability in the Linux kernel's Bluetooth management (mgmt) subsystem. The flaw stems from dereferencing RCU-protected pointers outside their critical sections and from missing reference counting on hci_conn structures used within mgmt_pending_cmd entries and hci_sync callbacks. A local attacker with low privileges can trigger race conditions that free the underlying connection object while other code paths still reference it. Successful exploitation can compromise kernel memory integrity, escalate privileges, or crash the system.

Critical Impact
Local low-privileged users can exploit a Bluetooth subsystem race condition to trigger a kernel use-after-free, potentially leading to privilege escalation or denial of service.

Affected Products

Linux kernel Bluetooth Host Controller Interface (HCI) management subsystem
Distributions shipping vulnerable kernel versions prior to the referenced stable fixes
Systems with Bluetooth hardware and CONFIG_BT enabled

Discovery Timeline

2026-08-10 - CVE-2026-68391 published to the National Vulnerability Database
2026-08-13 - Last updated in NVD database

Technical Details for CVE-2026-68391

Vulnerability Analysis

The vulnerability resides in the Linux kernel Bluetooth mgmt code that tracks pending management commands via mgmt_pending_cmd structures. These structures store pointers to hci_conn connection objects but do not hold a reference count on them. When the referenced hci_conn is freed by another kernel path while a pending command still holds the raw pointer, subsequent dereference triggers a use-after-free.

The defect is compounded by improper synchronization. RCU-protected pointers to hci_conn are dereferenced outside RCU read-side critical sections, violating the RCU contract. Additionally, accesses to conn->state occur without holding hdev->lock, producing data races that concurrent execution paths can exploit.

An attacker with local access and the ability to interact with Bluetooth interfaces can race socket operations and management commands to reach the freed-object window. Because kernel memory is corrupted, impact spans confidentiality, integrity, and availability.

Root Cause

The root cause is missing reference management and improper locking around hci_conn lifecycle handling in the Bluetooth management layer. Pending management commands cache raw pointers to connection objects without invoking hci_conn_get(), and callbacks scheduled through hci_sync execute after the connection may have been released.

Attack Vector

Exploitation requires local access with permission to open Bluetooth AF_BLUETOOTH sockets or invoke management IOCTLs. The attacker races connection teardown with pending management commands to dereference a freed hci_conn from a hci_sync callback. No user interaction is required. See the upstream commits at git.kernel.org b56f2eca and git.kernel.org da55f570 for the fix details.

Detection Methods for CVE-2026-68391

Indicators of Compromise

Kernel oops or panic messages referencing hci_conn, mgmt_pending_cmd, or hci_sync in dmesg or journalctl -k output
KASAN use-after-free reports pointing to Bluetooth management functions on kernels compiled with CONFIG_KASAN
Unexpected Bluetooth subsystem crashes correlating with local process activity on AF_BLUETOOTH sockets

Detection Strategies

Inventory kernel versions across the fleet and flag hosts running builds preceding the fix commits listed on kernel.org
Audit process telemetry for non-privileged users opening raw Bluetooth sockets or issuing management commands on servers where Bluetooth is not required
Enable KASAN and lockdep on test builds to surface race conditions during Bluetooth stress testing

Monitoring Recommendations

Forward kernel logs to a centralized SIEM and alert on repeated BUG: or general protection fault entries tagged with Bluetooth symbols
Monitor for module load events for bluetooth, btusb, and related drivers on systems where Bluetooth should remain disabled
Track privilege escalation and unexpected root shell spawns following Bluetooth-related crashes

How to Mitigate CVE-2026-68391

Immediate Actions Required

Apply the upstream stable kernel patches referenced by commits b56f2eca, d5b3b484, da55f570, ecdcb55e, and f915e74b from your distribution vendor
On systems that do not require Bluetooth, blacklist the bluetooth and btusb modules and disable the bluetooth.service unit
Restrict access to Bluetooth management interfaces by limiting membership in the bluetooth group and tightening D-Bus policies

Patch Information

The fix hardens the Bluetooth mgmt layer by acquiring hdev->lock for hci_conn lookups, taking a refcount on hci_conn pointers stored in mgmt_pending_cmd, and ensuring conn->state accesses are performed under the correct lock. See the five stable commits published on kernel.org, including b56f2eca, d5b3b484, da55f570, ecdcb55e, and f915e74b.

Workarounds

Disable the Bluetooth stack entirely on servers and workstations without Bluetooth requirements
Unload the bluetooth kernel module at runtime and prevent auto-load through modprobe configuration
Constrain untrusted local users from executing on hosts with active Bluetooth adapters until patches are deployed

bash

# Configuration example: disable Bluetooth stack until patched
sudo systemctl disable --now bluetooth.service
echo 'install bluetooth /bin/true' | sudo tee /etc/modprobe.d/blacklist-bluetooth.conf
echo 'install btusb /bin/true'     | sudo tee -a /etc/modprobe.d/blacklist-bluetooth.conf
sudo rmmod btusb bluetooth 2>/dev/null || true