CVE-2021-43400
📋 TL;DR
This vulnerability in BlueZ (Linux Bluetooth stack) allows a use-after-free condition when a client disconnects during D-Bus processing of a WriteValue call. Attackers could potentially execute arbitrary code or cause denial of service on affected systems. Systems running BlueZ 5.61 with Bluetooth enabled are vulnerable.
💻 Affected Systems
- BlueZ
- Linux distributions using BlueZ
📦 What is this software?
Bluez by Bluez
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to full system compromise, privilege escalation, or persistent backdoor installation
Likely Case
Denial of service causing Bluetooth service crashes or system instability
If Mitigated
Limited impact with proper network segmentation and Bluetooth disabled on critical systems
🎯 Exploit Status
Exploitation requires timing the client disconnection during specific D-Bus operations
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: BlueZ versions after commit 838c0dc7641e1c991c0f3027bf94bee4606012f8
Vendor Advisory: https://lists.debian.org/debian-lts-announce/2022/10/msg00026.html
Restart Required: Yes
Instructions:
1. Update BlueZ package using your distribution's package manager
2. For Debian/Ubuntu: sudo apt update && sudo apt upgrade bluez
3. Restart Bluetooth service: sudo systemctl restart bluetooth
4. Reboot system to ensure complete patch application
🔧 Temporary Workarounds
Disable Bluetooth Service
linuxTemporarily disable Bluetooth to prevent exploitation
sudo systemctl stop bluetooth
sudo systemctl disable bluetooth
Block Bluetooth Ports
linuxUse firewall to block Bluetooth network access
sudo ufw deny 22/tcp
sudo ufw deny 4711/tcp
🧯 If You Can't Patch
- Disable Bluetooth on all affected systems immediately
- Implement network segmentation to isolate Bluetooth-enabled devices
🔍 How to Verify
Check if Vulnerable:
Check BlueZ version: bluetoothd --version | grep -i '5.61'Check Version:
bluetoothd --version || dpkg -l | grep bluez || rpm -qa | grep bluezVerify Fix Applied:
Verify BlueZ version is newer than 5.61: bluetoothd --version📡 Detection & Monitoring
Log Indicators:
- Bluetooth service crashes in system logs
- D-Bus error messages related to WriteValue calls
- Unexpected Bluetooth disconnections
Network Indicators:
- Multiple rapid Bluetooth connection attempts
- Abnormal WriteValue request patterns
SIEM Query:
source="systemd" "bluetooth" AND ("crash" OR "segfault" OR "use-after-free")🔗 References
- https://git.kernel.org/pub/scm/bluetooth/bluez.git/commit/?id=838c0dc7641e1c991c0f3027bf94bee4606012f8
- https://lists.debian.org/debian-lts-announce/2022/10/msg00026.html
- https://git.kernel.org/pub/scm/bluetooth/bluez.git/commit/?id=838c0dc7641e1c991c0f3027bf94bee4606012f8
- https://lists.debian.org/debian-lts-announce/2022/10/msg00026.html
- https://lists.debian.org/debian-lts-announce/2024/09/msg00022.html
