CVE-2020-26558: Bluetooth Core Auth Bypass Vulnerability

CVE-2020-26558 Overview

CVE-2020-26558 is a man-in-the-middle vulnerability affecting the Passkey authentication procedure in Bluetooth LE and BR/EDR secure pairing implementations. This flaw exists in Bluetooth Core Specification versions 2.1 through 5.2, allowing a nearby attacker to identify the Passkey used during pairing by reflecting the public key and authentication evidence of the initiating device. The attacker can then complete authenticated pairing with the responding device using the determined Passkey.

Critical Impact

A nearby attacker can intercept and determine Bluetooth Passkey values bit-by-bit during pairing sessions, potentially allowing unauthorized device pairing and compromise of Bluetooth communications.

Affected Products

• Bluetooth Core Specification 2.1 through 5.2
• Linux Kernel (multiple versions)
• Intel Wireless Adapters (AX210, AX201, AX200, AC 9560, AC 9462, AC 9461, AC 9260, AC 8265, AC 8260, AC 3168, AC 7265, AC 3165, AX1675, AX1650, AC 1550)
• Fedora 34
• Debian Linux 9.0

Discovery Timeline

• May 24, 2021 - CVE-2020-26558 published to NVD
• November 4, 2025 - Last updated in NVD database

Technical Details for CVE-2020-26558

Vulnerability Analysis

This vulnerability exploits a weakness in the Passkey authentication procedure used during Bluetooth secure pairing. The flaw allows an attacker positioned within Bluetooth communication range to perform a man-in-the-middle attack by reflecting the public key and authentication evidence from the initiating device to the responding device. The attack methodology enables the attacker to determine the Passkey value one bit at a time through a process of reflection and analysis.

The vulnerability is classified under CWE-287 (Improper Authentication), as it fundamentally compromises the authentication mechanism that should ensure only authorized devices can pair. While physical proximity is required (adjacent network attack vector), the ability to systematically extract Passkey bits presents a significant risk for environments where Bluetooth pairing security is critical.

Root Cause

The root cause lies in the Bluetooth Core Specification's Passkey Entry authentication protocol design. The protocol does not adequately protect against reflection attacks where an attacker can mirror the initiating device's public key and authentication evidence back to the responding device. This design oversight allows the attacker to iteratively determine each bit of the Passkey by observing how the responding device reacts to the reflected authentication data.

The specification's reliance on the assumption that only the legitimate initiating device would possess the correct public key and authentication evidence proves insufficient against an attacker who can intercept and replay these values during the pairing handshake.

Attack Vector

The attack requires the adversary to be within Bluetooth communication range of both the initiating and responding devices during the pairing process. The attacker acts as a man-in-the-middle, intercepting the pairing session and reflecting cryptographic elements back to extract Passkey information.

The attack proceeds as follows: during a Passkey-authenticated pairing session, the attacker intercepts the public key exchange and authentication evidence from the initiating device. By reflecting these values to the responding device in a controlled manner, the attacker can observe responses that leak information about individual bits of the Passkey. This process is repeated until the complete Passkey is recovered, allowing the attacker to complete a valid authenticated pairing session.

Detection Methods for CVE-2020-26558

Indicators of Compromise

• Unexpected Bluetooth pairing failures followed by successful pairings from unknown devices
• Multiple Bluetooth pairing attempts within a short timeframe, potentially indicating bit-by-bit Passkey extraction
• Bluetooth device connections from previously unknown or untrusted MAC addresses
• Anomalous Bluetooth communication patterns during pairing procedures

Detection Strategies

• Monitor Bluetooth controller logs for unusual pairing session patterns or repeated authentication attempts
• Implement network monitoring solutions capable of detecting Bluetooth protocol anomalies in environments with sensitive devices
• Track and alert on new Bluetooth device pairings, especially in high-security environments
• Review system logs for Bluetooth-related errors or warnings during pairing operations

Monitoring Recommendations

• Enable verbose Bluetooth logging on critical systems to capture detailed pairing session information
• Implement asset inventory tracking for all authorized Bluetooth devices and alert on unauthorized pairings
• Consider deploying wireless intrusion detection systems (WIDS) capable of monitoring Bluetooth communications
• Regularly audit paired device lists on critical systems and remove any unrecognized devices

How to Mitigate CVE-2020-26558

Immediate Actions Required

• Update affected Intel wireless adapter firmware to patched versions as specified in Intel Security Advisory SA-00517 and SA-00520
• Apply kernel updates for Linux systems as referenced in distribution security advisories
• Review and remove any unknown or unauthorized Bluetooth pairings from affected devices
• Consider disabling Bluetooth on devices where it is not required until patches are applied

Patch Information

Multiple vendors have released security updates addressing this vulnerability. Intel has published firmware updates for affected wireless adapters through Intel Security Advisory SA-00517 and Intel Security Advisory SA-00520. Linux distributions including Debian and Fedora have released kernel updates addressing this issue. For Debian systems, refer to Debian Security Advisory DSA-4951 for patching guidance. Additional technical details are available from the CERT Vulnerability Advisory #799380.

Workarounds

• Disable Bluetooth functionality on systems where it is not essential for operations
• Conduct Bluetooth pairing only in physically secure environments where man-in-the-middle attacks are unlikely
• Use Bluetooth devices that support Secure Connections Only mode where available
• Implement strict physical access controls in environments where sensitive Bluetooth pairing may occur

# Disable Bluetooth on Linux systems
sudo systemctl stop bluetooth
sudo systemctl disable bluetooth

# Alternatively, blacklist 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