CVE-2026-31408: Linux Kernel Bluetooth Use-After-Free

CVE-2026-31408 Overview

CVE-2026-31408 is a use-after-free vulnerability in the Linux kernel's Bluetooth SCO (Synchronous Connection-Oriented) subsystem. The vulnerability exists in the sco_recv_frame() function, which reads conn->sk under sco_conn_lock() but immediately releases the lock without holding a reference to the socket. This race condition allows a concurrent close() operation to free the socket between the lock release and the subsequent sk->sk_state access, resulting in a use-after-free condition.

Critical Impact

A local attacker can exploit this race condition to cause kernel memory corruption, potentially leading to denial of service or arbitrary code execution with kernel privileges.

Affected Products

• Linux kernel (Bluetooth SCO subsystem)
• Linux systems with Bluetooth functionality enabled
• Kernel versions prior to the security patches

Discovery Timeline

• 2026-04-06 - CVE-2026-31408 published to NVD
• 2026-04-07 - Last updated in NVD database

Technical Details for CVE-2026-31408

Vulnerability Analysis

The use-after-free vulnerability stems from improper socket reference handling in the Bluetooth SCO subsystem. When sco_recv_frame() processes incoming SCO data, it accesses the socket pointer (conn->sk) while holding the sco_conn_lock(). However, the function releases this lock before performing operations that depend on the socket's validity, specifically before accessing sk->sk_state.

This creates a critical Time-of-Check Time-of-Use (TOCTOU) race window. During this window, another thread executing close() on the same socket can deallocate the socket structure. When the original thread subsequently attempts to access the freed socket memory, it triggers a use-after-free condition.

The kernel developers noted that other functions in the same file, such as sco_sock_timeout() and sco_conn_del(), correctly use sco_sock_hold() to safely maintain a reference under the lock, demonstrating the established pattern for safe socket reference handling in this codebase.

Root Cause

The root cause is a missing call to sco_sock_hold() before releasing the sco_conn_lock() in the sco_recv_frame() function. Without this reference increment, the socket can be freed by a concurrent operation while still being accessed. The fix involves using sco_sock_hold() to take a reference before releasing the lock and adding corresponding sock_put() calls on all exit paths to properly decrement the reference count.

Attack Vector

An attacker with local access to a Linux system with Bluetooth enabled could exploit this vulnerability by:

1. Establishing a Bluetooth SCO connection to the target system
2. Triggering concurrent socket receive and close operations
3. Timing the operations to hit the race condition window
4. Exploiting the resulting use-after-free for memory corruption or privilege escalation

The vulnerability requires local access and the ability to interact with Bluetooth subsystem APIs, but successful exploitation could result in kernel-level code execution or system denial of service.

Detection Methods for CVE-2026-31408

Indicators of Compromise

• Kernel oops or panic messages referencing sco_recv_frame() or related Bluetooth SCO functions
• Unexpected system crashes when Bluetooth SCO connections are active
• Memory corruption artifacts in kernel logs related to the Bluetooth subsystem
• KASAN (Kernel Address Sanitizer) reports indicating use-after-free in net/bluetooth/sco.c

Detection Strategies

• Deploy kernel memory debugging tools such as KASAN to detect use-after-free conditions in production or testing environments
• Monitor kernel logs for warnings or crashes associated with Bluetooth SCO subsystem functions
• Implement runtime integrity monitoring to detect unexpected kernel behavior patterns
• Use SentinelOne's kernel-level behavioral analysis to identify exploitation attempts targeting race conditions

Monitoring Recommendations

• Enable kernel debugging options such as CONFIG_DEBUG_KMEMLEAK and CONFIG_KASAN in test environments
• Configure syslog alerting for kernel warnings and panics related to Bluetooth modules
• Monitor Bluetooth connection activity for unusual patterns that may indicate exploitation attempts
• Deploy endpoint detection and response (EDR) solutions capable of identifying kernel-level anomalies

How to Mitigate CVE-2026-31408

Immediate Actions Required

• Update the Linux kernel to a patched version that includes the fix for CVE-2026-31408
• If immediate patching is not possible, consider disabling Bluetooth functionality on affected systems
• Review and restrict local access to systems where Bluetooth is required
• Monitor affected systems for signs of exploitation while patches are being deployed

Patch Information

The Linux kernel team has released patches addressing this vulnerability across multiple stable kernel branches. The fix involves adding proper socket reference counting using sco_sock_hold() before releasing the connection lock and ensuring sock_put() is called on all exit paths.

Patches are available in the following kernel commits:

• Kernel Git Commit 108b815
• Kernel Git Commit 45aaca9
• Kernel Git Commit 598dbba
• Kernel Git Commit 7197462
• Kernel Git Commit e76e8f0

Workarounds

• Disable Bluetooth functionality at the kernel level by blacklisting the bluetooth and btusb modules
• Restrict access to Bluetooth-related system calls using seccomp profiles or SELinux/AppArmor policies
• Implement network segmentation to limit Bluetooth exposure on critical systems
• Use physical Bluetooth disable switches where available on affected hardware

# Temporarily disable Bluetooth kernel modules
echo "blacklist bluetooth" >> /etc/modprobe.d/blacklist-bluetooth.conf
echo "blacklist btusb" >> /etc/modprobe.d/blacklist-bluetooth.conf
modprobe -r btusb bluetooth

# Verify Bluetooth modules are not loaded
lsmod | grep bluetooth