CVE-2023-51779: Linux Kernel Bluetooth Use-After-Free Flaw

CVE-2023-51779 Overview

CVE-2023-51779 is a use-after-free vulnerability in the Linux kernel's Bluetooth subsystem. The flaw exists in the bt_sock_recvmsg function within net/bluetooth/af_bluetooth.c and is triggered by a race condition in bt_sock_ioctl. This vulnerability affects Linux kernel versions through 6.6.8 and could allow a local attacker with low privileges to potentially achieve code execution or cause system instability.

Critical Impact

A local attacker can exploit a race condition in the Bluetooth socket implementation to trigger a use-after-free condition, potentially leading to privilege escalation or arbitrary code execution with kernel privileges.

Affected Products

• Linux Kernel through version 6.6.8
• Debian Linux (addressed in LTS announcement)
• Systems with Bluetooth subsystem enabled

Discovery Timeline

• 2024-02-29 - CVE CVE-2023-51779 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-51779

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free). The flaw resides in the Bluetooth socket handling code within the Linux kernel. When the bt_sock_recvmsg function processes incoming messages, a race condition can occur with concurrent bt_sock_ioctl operations. This race condition allows memory that has been freed to be subsequently accessed, creating a use-after-free scenario.

The attack requires local access to the system with low privileges. The exploitation complexity is high due to the race condition timing requirements. However, successful exploitation requires no user interaction and can result in complete compromise of confidentiality, integrity, and availability within the scope of the vulnerable component.

Root Cause

The root cause of CVE-2023-51779 is improper synchronization between the bt_sock_recvmsg and bt_sock_ioctl functions in the Bluetooth socket implementation. When these functions execute concurrently on the same socket object, the lack of proper locking mechanisms allows one execution path to free memory that another execution path is still referencing. This classic race condition pattern leads to the use-after-free condition.

Attack Vector

The attack vector for this vulnerability is local, requiring the attacker to have access to the target system. The attacker must be able to create and manipulate Bluetooth sockets, which typically requires CAP_NET_RAW capability or membership in appropriate groups. The attack involves:

1. Creating a Bluetooth socket connection
2. Triggering concurrent operations on bt_sock_recvmsg and bt_sock_ioctl
3. Exploiting the timing window to cause the use-after-free condition
4. Leveraging the freed memory access to potentially execute arbitrary code or escalate privileges

The vulnerability mechanism involves concurrent socket operations where one thread performs a receive operation via bt_sock_recvmsg while another thread simultaneously issues an ioctl call via bt_sock_ioctl. Due to insufficient locking, the ioctl operation may free socket-related data structures while the receive operation maintains a dangling reference. When the receive path subsequently accesses this freed memory, it can lead to kernel memory corruption. For detailed technical analysis, refer to the GitHub Linux Commit.

Detection Methods for CVE-2023-51779

Indicators of Compromise

• Unexpected kernel panics or system crashes related to the Bluetooth subsystem
• Kernel log messages indicating memory corruption in af_bluetooth.c or related Bluetooth modules
• Unusual Bluetooth socket activity from unprivileged processes
• KASAN (Kernel Address Sanitizer) reports showing use-after-free in Bluetooth code paths

Detection Strategies

• Monitor kernel logs for oops messages referencing bt_sock_recvmsg, bt_sock_ioctl, or af_bluetooth
• Deploy kernel runtime protection tools that can detect use-after-free memory access patterns
• Implement auditd rules to track Bluetooth socket creation and ioctl operations
• Use SentinelOne Singularity Platform to detect anomalous kernel-level behavior and exploitation attempts

Monitoring Recommendations

• Enable kernel debugging options such as KASAN when testing systems for this vulnerability
• Monitor for processes making unusual combinations of Bluetooth socket system calls
• Track kernel module loading events for Bluetooth-related modules
• Implement endpoint detection solutions capable of identifying kernel exploitation techniques

How to Mitigate CVE-2023-51779

Immediate Actions Required

• Update the Linux kernel to a patched version that includes commit 2e07e8348ea454615e268222ae3fc240421be768
• If immediate patching is not possible, disable the Bluetooth kernel module to eliminate the attack surface
• Review and restrict which users and processes have access to Bluetooth functionality
• Deploy SentinelOne agents to detect and prevent exploitation attempts at the endpoint level

Patch Information

The vulnerability has been addressed in the upstream Linux kernel. The fix is available in the commit referenced by the GitHub Linux Commit. Distribution-specific patches are available, including updates covered by the Debian LTS Announcement. Organizations should apply kernel updates from their respective Linux distribution vendors.

Workarounds

• Disable Bluetooth functionality at the kernel level by blacklisting the bluetooth module
• Restrict access to Bluetooth sockets by limiting CAP_NET_RAW capabilities
• Use kernel lockdown features to prevent unauthorized kernel modifications
• Implement network namespaces to isolate Bluetooth access for critical workloads

# Disable Bluetooth kernel module as a workaround
echo "blacklist bluetooth" | sudo tee /etc/modprobe.d/disable-bluetooth.conf
echo "blacklist btusb" | sudo tee -a /etc/modprobe.d/disable-bluetooth.conf
sudo modprobe -r bluetooth btusb