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VU#304725: Bluetooth implementations may not sufficiently validate elliptic curve parameters during Diffie-Hellman key exchange

CWE-325: Missing Required Cryptographic Step – CVE-2018-5383 Bluetooth utilizes a device pairing mechanism based on elliptic-curve Diffie-Hellman (ECDH) key exchange to allow encrypted communication between devices. The ECDH key pair consists of a private and a public key, and the public keys are exchanged to produce a shared pairing key. The devices must also agree on the elliptic curve parameters being used. Previous work on the “Invalid Curve Attack” showed that the ECDH parameters are not always validated before being used in computing the resulted shared key, which reduces attacker effort to obtain the private key of the device under attack if the implementation does not validate all of the parameters before computing the shared key. In some implementations, the elliptic curve parameters are not all validated by the cryptographic algorithm implementation, which may allow a remote attacker within wireless range to inject an invalid public key to determine the session key with high probability. Such an attacker can then passively intercept and decrypt all device messages, and/or forge and inject malicious messages. Both Bluetooth low energy (LE) implementations of Secure Connections Pairing in operating system software and BR/EDR implementations of Secure Simple Pairing in device firmware may be affected. Bluetooth device users are encouraged to consult with their device vendor for further information. Since the vulnerability was identified, the Bluetooth SIG has updated the Bluetooth specifications to require validation of any public key received as part of public key-based security procedures, thereby providing a remedy to the vulnerability from a specification perspective. In addition, the Bluetooth SIG has added testing for this vulnerability within its Bluetooth Qualification Program. The Bluetooth SIG has also released a public statement regarding the vulnerability. More information can be found on the researchers’ website.

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