CVE-2020-10135: Bluetooth Core Auth Bypass Vulnerability

CVE-2020-10135 Overview

CVE-2020-10135 is a protocol-level vulnerability in the Bluetooth BR/EDR (Basic Rate/Enhanced Data Rate) Core Specification affecting versions 5.2 and earlier. This flaw, known as the Bluetooth Impersonation AttackS (BIAS) vulnerability, allows an unauthenticated attacker with adjacent network access to bypass authentication during the pairing process. An attacker can impersonate either a Bluetooth BR/EDR master or slave device to establish a connection with a previously paired remote device without knowing the link key.

Critical Impact

Attackers within Bluetooth range can impersonate trusted devices and bypass authentication, potentially gaining unauthorized access to paired devices and sensitive data.

Affected Products

• Bluetooth BR/EDR Core Specification v5.2 and earlier
• openSUSE Leap 15.1
• Any device implementing vulnerable Bluetooth BR/EDR protocol versions

Discovery Timeline

• 2020-05-19 - CVE-2020-10135 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-10135

Vulnerability Analysis

The BIAS vulnerability exploits fundamental weaknesses in how Bluetooth BR/EDR handles legacy pairing and secure-connections pairing authentication. The core issue lies in the authentication procedure between previously paired devices, where the protocol fails to properly verify that both parties possess the shared link key before completing authentication.

When two Bluetooth devices have previously paired, they store a shared secret called the link key. During subsequent connections, authentication should verify that both devices possess this key. However, the vulnerability allows an attacker to bypass this verification by manipulating the authentication protocol flow, specifically by exploiting the lack of mandatory mutual authentication and role-switching protections.

Root Cause

The vulnerability stems from two primary weaknesses in the Bluetooth BR/EDR specification (CWE-757: Selection of Less-Secure Algorithm During Negotiation, CWE-290: Authentication Bypass by Spoofing):

1. Lack of Mandatory Mutual Authentication: The Bluetooth BR/EDR specification does not require mutual authentication during secure connection establishment. An attacker can complete authentication without proving possession of the link key by manipulating the authentication direction.

2. Role-Switching During Authentication: The protocol allows role-switching (master/slave) after authentication has started but before it completes. An attacker can exploit this to avoid being authenticated while still completing the overall authentication procedure.

Attack Vector

The attack requires adjacent network access, meaning the attacker must be within Bluetooth radio range (typically 10-100 meters) of the target devices. The attack flow involves:

1. The attacker identifies two previously paired Bluetooth devices
2. The attacker impersonates one device (either master or slave) to the other
3. By manipulating authentication direction and exploiting role-switching, the attacker completes authentication without knowing the link key
4. Once authenticated, the attacker can access services provided by the target device

The attack does not require user interaction and can be performed against devices in discoverable or non-discoverable mode, as long as the attacker knows the Bluetooth address of the target device.

Detection Methods for CVE-2020-10135

Indicators of Compromise

• Unexpected Bluetooth connection attempts from known device addresses
• Authentication failures followed by successful connections from the same device address
• Role-switch events during authentication procedures
• Connections from devices that should be physically distant or powered off

Detection Strategies

• Monitor Bluetooth logs for anomalous authentication patterns and role-switching during pairing
• Implement Bluetooth intrusion detection systems that track device behavior baselines
• Deploy network monitoring tools capable of analyzing Bluetooth traffic in critical environments
• Correlate physical presence of devices with Bluetooth connection events

Monitoring Recommendations

• Enable verbose Bluetooth logging on critical systems and endpoints
• Review the CERT Vulnerability Report for detailed detection guidance
• Implement alerting for multiple failed authentication attempts followed by success
• Monitor for unexpected Bluetooth connections in high-security environments

How to Mitigate CVE-2020-10135

Immediate Actions Required

• Apply firmware updates from device manufacturers that address the BIAS vulnerability
• Disable Bluetooth on devices where it is not required for business operations
• Reduce Bluetooth discoverability and visibility settings where possible
• Review and remove unused Bluetooth pairings from critical devices

Patch Information

The Bluetooth Special Interest Group (Bluetooth SIG) has updated the Bluetooth Core Specification to require mutual authentication for legacy authentication and secure connections authentication. Device manufacturers have released firmware updates addressing this vulnerability. Consult the Bluetooth BIAS Vulnerability Overview for official guidance and the openSUSE Security Announcements for Linux-specific patches.

Workarounds

• Disable Bluetooth functionality when not actively in use
• Use Bluetooth only in secure, controlled environments where physical proximity attacks are less feasible
• Implement application-level encryption and authentication for sensitive data transmitted over Bluetooth
• Consider using alternative communication methods for high-security applications

For detailed technical analysis of the vulnerability, refer to the GitHub Analysis on BIAS which provides comprehensive information about the attack methodology and mitigation approaches.