CVE-2026-31511: Linux Kernel Use-After-Free Vulnerability

CVE-2026-31511 Overview

A dangling pointer vulnerability has been identified in the Linux kernel's Bluetooth Management (MGMT) subsystem. The flaw exists in the mgmt_add_adv_patterns_monitor_complete function where improper condition checking leads to premature memory deallocation without proper list unlinking. When mgmt_pending_free(cmd) is called and status != -ECANCELED, the function performs kfree(cmd) without first unlinking the command structure from the pending operations list, resulting in a dangling pointer that can be dereferenced during subsequent list traversals.

Critical Impact
This vulnerability can lead to use-after-free conditions when subsequent list traversal operations (such as mgmt_pending_foreach during __mgmt_power_off or additional mgmt_pending_valid calls) dereference the freed memory, potentially causing kernel crashes or memory corruption.

Affected Products

Linux Kernel (Bluetooth MGMT subsystem)
Systems utilizing Linux Bluetooth stack with advertisement pattern monitoring functionality

Discovery Timeline

2026-04-22 - CVE CVE-2026-31511 published to NVD
2026-04-23 - Last updated in NVD database

Technical Details for CVE-2026-31511

Vulnerability Analysis

The vulnerability resides in the Bluetooth Management interface of the Linux kernel, specifically within the advertisement pattern monitoring completion handler. The core issue stems from an incorrect conditional check that determines whether mgmt_pending_valid should be executed before freeing the command structure.

When processing the completion of an advertisement patterns monitor request, the function needs to properly manage the lifecycle of command structures stored in a linked list. The flawed logic fails to call mgmt_pending_valid in scenarios where the status is not -ECANCELED, resulting in mgmt_pending_free(cmd) being called directly. This call frees the memory associated with the command structure via kfree(cmd) without first removing the node from the pending operations list.

The consequence is a classic dangling pointer scenario where the linked list still contains a reference to now-freed memory. Any subsequent operations that traverse this list—such as mgmt_pending_foreach invoked during Bluetooth power-off sequences or additional validity checks via mgmt_pending_valid—will attempt to access the deallocated memory region.

Root Cause

The root cause is an incorrect conditional statement in the mgmt_add_adv_patterns_monitor_complete function. The condition that guards the call to mgmt_pending_valid does not properly account for all status values, causing the function to skip the necessary list unlinking step before memory deallocation. The fix ensures that mgmt_pending_valid is executed whenever the status is not -ECANCELED, guaranteeing proper list management before the command structure is freed.

Attack Vector

The attack vector for this vulnerability is local, requiring access to the Bluetooth subsystem on the affected Linux system. An attacker would need to trigger specific Bluetooth MGMT operations that result in the vulnerable code path being executed. The exploitation typically involves:

Initiating advertisement pattern monitoring operations through the Bluetooth MGMT interface
Triggering completion handlers with specific status conditions that bypass the validity check
Subsequently causing list traversal operations that dereference the freed memory

The vulnerability primarily manifests during Bluetooth power management operations or when multiple MGMT operations are pending simultaneously.

Detection Methods for CVE-2026-31511

Indicators of Compromise

Kernel panic or system crashes during Bluetooth operations, particularly during power-off sequences
Memory corruption errors reported in kernel logs related to Bluetooth MGMT subsystem
Unexpected behavior when using Bluetooth advertisement pattern monitoring features
KASAN (Kernel Address Sanitizer) reports indicating use-after-free in Bluetooth code paths

Detection Strategies

Monitor kernel logs for memory corruption warnings or crashes in the net/bluetooth/mgmt.c module
Enable KASAN on development or test systems to detect use-after-free access patterns
Implement system monitoring for unexpected Bluetooth daemon crashes or restarts
Review kernel crash dumps for stack traces involving mgmt_pending_foreach or mgmt_pending_valid

Monitoring Recommendations

Configure kernel crash reporting tools (kdump, crash) to capture and analyze Bluetooth-related kernel panics
Enable enhanced Bluetooth subsystem logging during troubleshooting periods
Monitor system stability metrics on systems with active Bluetooth advertisement monitoring
Deploy endpoint detection solutions capable of identifying kernel memory corruption anomalies

How to Mitigate CVE-2026-31511

Immediate Actions Required

Apply the Linux kernel patches addressing CVE-2026-31511 as soon as they become available for your distribution
Prioritize patching on systems that actively use Bluetooth advertisement pattern monitoring functionality
Consider temporarily disabling Bluetooth functionality on critical systems until patches are applied
Review system logs for any signs of exploitation or related crashes

Patch Information

The Linux kernel development team has released patches to address this vulnerability. The fix corrects the conditional logic in mgmt_add_adv_patterns_monitor_complete to ensure mgmt_pending_valid is properly called before freeing command structures.

Patches are available through the following kernel commits:

System administrators should update their Linux kernel to a version containing these fixes and reboot the system to apply the changes.

Workarounds

Disable Bluetooth functionality at the kernel level using rfkill block bluetooth if Bluetooth is not required
Restrict access to Bluetooth MGMT interfaces by limiting user permissions to the Bluetooth subsystem
Consider using kernel live patching solutions if available for your distribution to apply fixes without immediate reboot
Implement network segmentation to limit exposure of systems that cannot be immediately patched

bash

# Temporarily disable Bluetooth on Linux systems
rfkill block bluetooth

# Verify Bluetooth is blocked
rfkill list bluetooth

# To re-enable after patching
rfkill unblock bluetooth