CVE-2023-24023: Bluetooth Core Specification RCE Flaw

CVE-2023-24023 Overview

CVE-2023-24023, also known as BLUFFS (Bluetooth Forward and Future Secrecy), is a critical protocol-level vulnerability affecting Bluetooth BR/EDR (Basic Rate/Enhanced Data Rate) devices implementing Secure Simple Pairing and Secure Connections pairing. This vulnerability exists in the Bluetooth Core Specification versions 4.2 through 5.4 and enables man-in-the-middle (MITM) attacks that can force the negotiation of a short encryption key length. Successful exploitation may lead to discovery of the encryption key and enable live traffic injection into encrypted Bluetooth sessions.

The vulnerability stems from fundamental weaknesses in the Bluetooth session establishment process, where an attacker within adjacent network proximity can manipulate the key negotiation protocol to downgrade cryptographic protections. This affects billions of devices across consumer electronics, enterprise systems, and IoT deployments worldwide.

Critical Impact

Attackers can perform man-in-the-middle attacks to force weak encryption keys, potentially allowing decryption of Bluetooth communications and live injection of malicious data across paired devices.

Affected Products

• Bluetooth Core Specification 4.2 through 5.4
• Microsoft Windows 10 1809, 21H2, 22H2
• Microsoft Windows 11 21H2, 22H2, 23H2
• Microsoft Windows Server 2019
• Microsoft Windows Server 2022, 2022 23H2

Discovery Timeline

• 2023-11-28 - CVE-2023-24023 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-24023

Vulnerability Analysis

The BLUFFS vulnerability represents a fundamental flaw in how Bluetooth BR/EDR devices negotiate session keys during the pairing and connection establishment process. The attack targets the Secure Simple Pairing (SSP) and Secure Connections (SC) pairing mechanisms that were designed to provide stronger security guarantees for Bluetooth communications.

During a Bluetooth session establishment, devices negotiate encryption parameters including key length. The vulnerability allows an adjacent attacker to manipulate this negotiation process, forcing both legitimate devices to accept a significantly shorter encryption key than intended. With a reduced key length, the attacker can then perform cryptanalytic attacks to recover the session key.

Once the encryption key is compromised, the attacker gains the ability to decrypt ongoing communications between the paired devices and inject arbitrary data into the encrypted session in real-time. This breaks both the confidentiality and integrity guarantees that Bluetooth encryption is designed to provide.

Root Cause

The root cause of CVE-2023-24023 lies in insufficient enforcement of minimum key length requirements during the Bluetooth session key derivation process. The Bluetooth Core Specification versions 4.2 through 5.4 do not mandate strong enough protections against key length downgrade attacks during session establishment.

Specifically, the protocol allows for negotiation of session key parameters without adequate authentication of the negotiation messages themselves. This permits an attacker positioned between two legitimate devices to tamper with the key length negotiation, forcing both endpoints to derive a weaker session key than either device would normally accept.

The vulnerability also impacts forward and future secrecy properties, as compromised session keys from one session could potentially be leveraged to attack subsequent sessions or reveal information about previously encrypted communications.

Attack Vector

The attack requires the adversary to be within Bluetooth radio range of the target devices, representing an adjacent network attack vector. The attacker must be able to intercept and modify Bluetooth protocol messages during the session establishment phase.

The attack proceeds through the following stages:

1. The attacker positions themselves within Bluetooth range of two devices attempting to establish a secure connection
2. During the session key negotiation phase, the attacker intercepts and modifies protocol messages to force a shorter key length
3. Both legitimate devices unknowingly derive a weak session key based on the manipulated parameters
4. The attacker performs cryptanalysis on the captured encrypted traffic to recover the weak session key
5. With the recovered key, the attacker can decrypt communications and inject malicious data into the session

The attack complexity is considered high as it requires precise timing and specialized equipment to intercept and manipulate Bluetooth protocol messages in real-time. However, no user interaction is required once the attacker is in position.

Detection Methods for CVE-2023-24023

Indicators of Compromise

• Unexpected Bluetooth disconnections and re-pairing requests between previously paired devices
• Anomalous Bluetooth radio activity patterns indicating potential protocol manipulation
• Detection of unknown Bluetooth devices in close proximity during sensitive communications
• Degraded encryption strength indicators reported by Bluetooth stack implementations

Detection Strategies

• Monitor Bluetooth Host Controller Interface (HCI) logs for anomalous session establishment patterns or repeated negotiation attempts
• Implement Bluetooth intrusion detection systems capable of identifying protocol-level manipulation attempts
• Deploy radio frequency monitoring tools to detect suspicious Bluetooth activity in sensitive environments
• Configure endpoint detection to alert on Bluetooth stack anomalies or unexpected pairing behaviors

Monitoring Recommendations

• Enable detailed Bluetooth logging on critical systems to capture session establishment parameters
• Regularly audit paired device lists on enterprise endpoints to identify unauthorized pairings
• Implement physical security controls in high-security areas to limit potential attacker proximity
• Monitor for security advisories from device manufacturers regarding BLUFFS mitigation updates

How to Mitigate CVE-2023-24023

Immediate Actions Required

• Apply vendor security patches that address the BLUFFS vulnerability as they become available
• Consider disabling Bluetooth functionality on systems where it is not essential for operations
• Implement strict Bluetooth pairing policies, limiting connections to known and trusted devices only
• Conduct pairing operations in secure, physically controlled environments to reduce MITM risk

Patch Information

The Bluetooth SIG has acknowledged this vulnerability and published guidance for implementers. Microsoft has released security updates addressing this vulnerability in affected Windows versions. Organizations should monitor vendor advisories and apply patches as they become available for their specific devices and operating systems.

For detailed information, consult the Bluetooth SIG BLUFFS Vulnerability Advisory and the ACM Research Paper documenting the vulnerability.

Workarounds

• Disable Bluetooth functionality on devices handling sensitive communications until patches are applied
• Use alternative secure communication channels (wired connections, Wi-Fi with WPA3) for sensitive data transfer
• Implement application-layer encryption for sensitive data transmitted over Bluetooth connections
• Restrict Bluetooth visibility and discoverability modes to reduce exposure to potential attackers

# Windows: Disable Bluetooth service temporarily
Stop-Service -Name "bthserv" -Force
Set-Service -Name "bthserv" -StartupType Disabled

# Re-enable after patching
Set-Service -Name "bthserv" -StartupType Automatic
Start-Service -Name "bthserv"