CVE-2020-24490: BlueZ Denial of Service Vulnerability

CVE-2020-24490 Overview

CVE-2020-24490 is a buffer restriction vulnerability in BlueZ, the official Linux Bluetooth protocol stack, that allows an unauthenticated attacker to potentially cause a denial of service condition via adjacent network access. This vulnerability affects all Linux kernel versions that support BlueZ, making it a widespread concern for Linux-based systems with Bluetooth functionality enabled.

Critical Impact

Unauthenticated attackers within Bluetooth range can exploit improper buffer restrictions to crash vulnerable systems, disrupting Bluetooth services and potentially affecting system stability.

Affected Products

• BlueZ (all versions)
• Linux Kernel (versions supporting BlueZ)
• Systems with Bluetooth Low Energy (BLE) 5 support

Discovery Timeline

• February 2, 2021 - CVE-2020-24490 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-24490

Vulnerability Analysis

This vulnerability stems from improper buffer restrictions within the BlueZ Bluetooth stack implementation in the Linux kernel. The flaw allows an unauthenticated user in adjacent proximity (within Bluetooth range) to send specially crafted Bluetooth packets that exploit the buffer handling weakness.

The attack requires no authentication and can be executed without user interaction, making it particularly concerning for devices operating in public or shared spaces. The vulnerability specifically targets the availability of the system, with no direct impact on confidentiality or integrity. An attacker can leverage this flaw to cause a denial of service condition, potentially crashing Bluetooth services or requiring system restarts to restore functionality.

This vulnerability is particularly relevant to systems utilizing Bluetooth 5 capabilities, where extended advertising data may trigger the improper buffer handling condition.

Root Cause

The root cause of CVE-2020-24490 lies in improper buffer restrictions within the BlueZ protocol stack's data handling routines. When processing certain Bluetooth packets, the code fails to properly validate or restrict buffer operations, allowing malformed or oversized data to trigger an error condition that leads to service disruption.

The vulnerability is classified under CWE as having insufficient information for specific categorization, but the behavior is consistent with improper input validation and buffer management issues common in protocol implementations.

Attack Vector

The attack vector for this vulnerability is adjacent network access, meaning an attacker must be within Bluetooth radio range of the target device to exploit the vulnerability. Key characteristics of the attack vector include:

• Adjacent Network Access: Attacker must be in physical proximity (typical Bluetooth range of 10-100 meters depending on class)
• No Authentication Required: The vulnerability can be exploited without any credentials or prior access
• No User Interaction: Exploitation does not require any action from the victim user
• Availability Impact: Successful exploitation results in denial of service affecting Bluetooth functionality

The attack leverages improper buffer restrictions in the Bluetooth stack to send malicious packets that cause the service to fail. Since the vulnerability exists in the kernel-level BlueZ implementation, the impact may extend beyond just Bluetooth services depending on system configuration.

Detection Methods for CVE-2020-24490

Indicators of Compromise

• Unexpected Bluetooth service crashes or restarts on Linux systems
• System logs showing BlueZ-related errors or kernel panics in Bluetooth subsystem
• Repeated connection attempts from unknown Bluetooth devices in close proximity
• Increased Bluetooth-related error messages in dmesg or journalctl output

Detection Strategies

• Monitor system logs for BlueZ service failures and Bluetooth subsystem errors
• Implement network-level monitoring for anomalous Bluetooth traffic patterns
• Deploy endpoint detection rules that identify unusual Bluetooth stack behavior
• Use kernel auditing to track Bluetooth-related system calls and potential exploitation attempts

Monitoring Recommendations

• Enable verbose logging for the BlueZ service to capture detailed connection attempts
• Configure system monitoring to alert on Bluetooth service restarts or crashes
• Implement baseline monitoring for normal Bluetooth activity to identify anomalies
• Review hcidump captures periodically for suspicious Bluetooth packet patterns

How to Mitigate CVE-2020-24490

Immediate Actions Required

• Apply the latest Linux kernel security updates that address CVE-2020-24490
• If Bluetooth functionality is not required, disable Bluetooth services using systemctl disable bluetooth
• Update the BlueZ package to the latest patched version available for your distribution
• Limit physical access to sensitive systems to reduce adjacent network attack exposure

Patch Information

Intel has released a security advisory addressing this vulnerability. System administrators should apply kernel patches that include fixes for the BlueZ buffer restriction issue. For detailed patch information, refer to Intel Security Advisory SA-00435.

Check with your Linux distribution's security update channels for specific kernel versions that include the fix:

• Debian/Ubuntu: Check apt changelog linux-image-$(uname -r) for security fixes
• RHEL/CentOS: Review kernel changelogs via rpm -q --changelog kernel
• Fedora: Use dnf changelog kernel to verify patch status

Workarounds

• Disable Bluetooth on systems where it is not required using rfkill block bluetooth
• Implement physical security measures to limit adjacent network access to critical systems
• Use Bluetooth device whitelisting where supported to restrict connections to known devices
• Consider network segmentation for IoT and embedded devices with Bluetooth capabilities

# Configuration example - Disable Bluetooth on Linux systems
# Add to /etc/modprobe.d/bluetooth-blacklist.conf
blacklist bluetooth
blacklist btusb
blacklist btrtl
blacklist btbcm
blacklist btintel

# Alternatively, use rfkill to block Bluetooth
rfkill block bluetooth

# Verify Bluetooth is disabled
rfkill list bluetooth