Many modern Bluetooth devices use the Bluetooth Basic Rate/Enhanced Data Rate (BR/EDR) technology that allows secure communication between devices. Bluetooth Core Specification 4.2 through 5.4 introduced Secure Simple Pairing (SSP) and Secure Connections (SC) pairing to improve security. However, a recent vulnerability (CVE-2023-24023) has been discovered that affects these devices, allowing certain man-in-the-middle (MITM) attacks to force a short key length. This may potentially lead to the discovery of the encryption key and live injection, also known as the Bluetooth Low Energy Utility Forging Short Secrets (BLUFFS) attack. In this article, we will explore this vulnerability, its impact, and potential solutions.

Code Snippet: Demonstration of MITM Attack Vector

    ...
    def setup_fake_gatt_server(self):
        server = BluetoothServer()
        service = MyFakeService(server, "DemoService", GattServiceTypes.LOCATION)

        # Add the characteristic we want to MITM
        location_char = MyFakeCharacteristic(service, "Location", GattCharacteristicTypes.LOCATION)
        self.key_sync_char = KeySyncCharacteristic(service, "KeySync")
        service.add_characteristic(location_char)
        service.add_characteristic(self.key_sync_char)

        server.add_service(service)

        # Set up a malicious MITM device acting as a GATT server
        print("Setup Fake GATT Server")
        self.fake_device = MyFakeDevice(server=server, name='MITM_Attacker', device_address=self.fake_address)
        self.fake_device.advertise()
    ...

Before diving into the details, let us first understand the terms and technologies involved in this vulnerability:

- Bluetooth BR/EDR: It is a wireless technology for exchanging data over short distances between devices.
- Secure Simple Pairing (SSP): It is a security protocol that allows pairing of devices using cryptographic keys.
- Secure Connections (SC) pairing: A stronger and secure form of SSP that improves the encryption and security of connecting devices.

How Does the BLUFFS Attack Work?

In a normal scenario, Bluetooth devices securely pair using SSP or SC pairing protocols. The pairing process consists of exchanging cryptographic keys that ensure a secure and encrypted connection. However, the BLUFFS attack involves an intermediate device (the attacker) that intercepts the pairing process and manipulates the exchange of keys between the devices. As a result, the attacker can force a shorter key length that weakens the encryption, making it easier to crack for the attacker.

The attacker calculates the encryption key using the weaker, shorter key length.

4. Once the key is obtained, the attacker can perform live injection and tamper with the data exchanged between the devices.

Original References

The BLUFFS attack was first discovered and reported by researchers. You can find their original paper here:
- "BLUFFS: Practical Key Reinstallation Attacks in Bluetooth" Link to paper

Additionally, the Bluetooth Special Interest Group (SIG) has acknowledged this vulnerability and has issued a security notice with more details:
- "Security Notice: Bluetooth Pairing Vulnerability" Link to security notice

Exploit Details

As mentioned earlier, the BLUFFS attack allows a MITM attacker to manipulate key exchange information during the pairing process of Bluetooth devices. This can lead to several possible exploits:

1. Live Injection: The attacker can intercept and modify the data being exchanged between the devices, which can lead to various attacks such as data corruption, fake updates, or unauthorized actions.
2. Data Decryption: Since the attacker has access to the encryption key, they can decrypt any data transferred between the affected devices, potentially exposing sensitive and confidential information.

To address and prevent the BLUFFS attack, the following steps can be taken

1. Keep devices up-to-date: Make sure that your Bluetooth devices are running the latest firmware and operating system updates, as they may contain patches for the vulnerability.
2. Disable Bluetooth when not in use: Turning off Bluetooth when it is not being used can minimize the risk of an attacker intercepting your device's pairing process.
3. Use longer key lengths: If possible, configure your devices to use longer key lengths when pairing. This can make it more difficult for an attacker to crack the encryption key.
4. Be cautious of pairing in public: Avoid pairing your Bluetooth devices in crowded public areas where an attacker might try to intercept the pairing process.

In conclusion, the CVE-2023-24023 vulnerability or the BLUFFS attack is a significant concern for Bluetooth BR/EDR devices using Secure Simple Pairing and Secure Connections pairing in Bluetooth Core Specification 4.2 through 5.4. By understanding the underlying mechanisms and adopting preventive measures, you can protect your devices from potential MITM attacks and ensure secure communication.

Timeline

Published on: 11/28/2023 07:15:41 UTC
Last modified on: 12/02/2023 04:40:02 UTC