CVE-2020-0556: BlueZ Privilege Escalation Vulnerability

CVE-2020-0556 Overview

CVE-2020-0556 is an improper access control vulnerability in the BlueZ Bluetooth protocol stack affecting versions prior to 5.54. This flaw allows an unauthenticated attacker within adjacent network range to potentially escalate privileges and cause denial of service conditions on affected Linux systems.

Critical Impact

Unauthenticated attackers within Bluetooth range can exploit this vulnerability to gain elevated privileges or disrupt system availability without any user interaction required.

Affected Products

• BlueZ versions prior to 5.54
• Canonical Ubuntu Linux 16.04 LTS, 18.04 LTS, 19.10
• Debian Linux 8.0, 9.0, 10.0
• openSUSE Leap 15.1, 15.2

Discovery Timeline

• March 12, 2020 - CVE-2020-0556 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-0556

Vulnerability Analysis

This vulnerability exists within the BlueZ Bluetooth subsystem, which is the official Linux Bluetooth protocol stack. The improper access control flaw occurs in how BlueZ handles certain Bluetooth operations, failing to properly validate authorization before permitting sensitive actions.

The vulnerability requires adjacent network access, meaning an attacker must be within Bluetooth radio range (typically up to 100 meters for Class 1 devices) to exploit the flaw. Once in range, the attacker can interact with vulnerable BlueZ services without authentication, potentially leading to privilege escalation or denial of service conditions.

The scope of this vulnerability is changed, meaning a successful exploit can affect resources beyond the vulnerable component itself, potentially impacting other system components or connected devices.

Root Cause

The root cause of CVE-2020-0556 is improper access control within the BlueZ subsystem. The vulnerable code fails to properly enforce authorization checks before allowing certain Bluetooth operations. This allows unauthenticated users within adjacent network range to bypass intended security restrictions and perform actions that should require proper authentication or authorization.

Attack Vector

The attack vector for this vulnerability is adjacent network access via Bluetooth. An attacker must be within Bluetooth range of the target system to exploit the flaw. The attack has low complexity, requires no privileges, and does not depend on user interaction.

The exploitation scenario involves:

1. An attacker positions themselves within Bluetooth range of a vulnerable Linux system running BlueZ versions prior to 5.54
2. The attacker sends specially crafted Bluetooth requests to the target system
3. Due to improper access control, the BlueZ subsystem processes these requests without proper authorization validation
4. This can result in privilege escalation, allowing the attacker to gain elevated access, or denial of service, disrupting system availability

The vulnerability affects the confidentiality, integrity, and availability of the target system, though each impact is limited in scope.

Detection Methods for CVE-2020-0556

Indicators of Compromise

• Unexpected Bluetooth connection attempts from unknown devices
• Anomalous BlueZ daemon behavior or crashes
• Unusual privilege escalation events correlated with Bluetooth activity
• System instability or denial of service conditions when Bluetooth is active

Detection Strategies

• Monitor BlueZ daemon (bluetoothd) logs for unusual connection patterns or error messages
• Implement endpoint detection rules for suspicious Bluetooth activity on Linux systems
• Audit system logs for privilege escalation events that may correlate with Bluetooth connections
• Deploy SentinelOne agents on Linux endpoints to detect exploitation attempts

Monitoring Recommendations

• Enable verbose logging for the BlueZ Bluetooth subsystem
• Configure alerts for unexpected Bluetooth device pairing attempts
• Monitor system resource utilization for denial of service indicators
• Review journalctl -u bluetooth output regularly for anomalous activity

How to Mitigate CVE-2020-0556

Immediate Actions Required

• Update BlueZ to version 5.54 or later immediately
• Disable Bluetooth on systems where it is not required
• Restrict physical access to prevent attackers from entering Bluetooth range
• Apply vendor security patches from your Linux distribution

Patch Information

Multiple Linux distributions have released security updates to address this vulnerability:

• Ubuntu: Security updates available via Ubuntu Security Notice USN-4311-1
• Debian: Patches available via Debian DSA-4647 and Debian LTS Security Announcement
• openSUSE: Updates released via openSUSE Security Announcement
• Gentoo: Security advisory available at GLSA 202003-49
• Intel: Advisory published at Intel Security Advisory SA-00352

Workarounds

• Disable Bluetooth functionality entirely if not needed using systemctl disable bluetooth and systemctl stop bluetooth
• Use physical Bluetooth hardware switches to disable radio when not in use
• Implement network segmentation to limit Bluetooth-enabled devices in sensitive environments
• Consider using USB Bluetooth adapters that can be physically removed when not needed

# Disable BlueZ Bluetooth service as a workaround
sudo systemctl stop bluetooth
sudo systemctl disable bluetooth

# Verify Bluetooth is disabled
sudo systemctl status bluetooth

# Block Bluetooth kernel modules
echo "blacklist btusb" | sudo tee /etc/modprobe.d/bluetooth-blacklist.conf
echo "blacklist bluetooth" | sudo tee -a /etc/modprobe.d/bluetooth-blacklist.conf