Bluetooth BIAS Attack

A new attack dubbed Bluetooth BIAS attack allows attackers to spoof the already paired device and to successfully authenticate without having the link key that used for pairing.

Researchers from École Polytechnique Fédérale de Lausanne (EPFL) published a paper named BIAS: Bluetooth Impersonation AttackS details that Bluetooth standard contains vulnerabilities enabling an attacker to impersonate a device and to establish a secure connection.

Bluetooth BIAS Attack

The BIAS attack is due to the flaws in the Bluetooth specification so that any standard-compliant Bluetooth device found to be vulnerable.

Researchers checked the attack against Cypress, Qualcomm, Apple, Intel, Samsung, and CSR, they all found to be vulnerable.


For this attack to be successful the attacking device needs to be within the range of a vulnerable Bluetooth device that has previously established a BR/EDR bonding with a remote device with a Bluetooth address known to the attacker.

In the paper published researchers derived two attack methods, with the Secure Connections mode, the attacker needs to be a previously paired remote device but with no support for Secure Connections thereby downgrading the authentication security.

This would allow an attacker with the BIAS method against the legacy authentication unless the device they are attacking is in Secure Connections only mode.

“If the attacker can either downgrade authentication or is attacking a device that does not support Secure Connections, they can perform the attack using a similar method by initiating a master-slave role switch to place itself into the master role and become the authentication initiator,” reads vulnerability note.

If the attack is successful they can authentication with the remote device. If the attacked device does not mutually authenticate with attackers device in the master role, it will still result in authentication-complete notification even though the link key not shared.

As a result of a BIAS attack, an attacker completes secure connection establishment while impersonating Bluetooth master and slave devices, without having to know and authenticate the long term key shared between the victims.


To fix the vulnerability, Bluetooth SIG is to update the Bluetooth Core Specification to distinguish “when role switches are permitted, to require mutual authentication in legacy authentication, and to recommend checks for encryption-type to avoid a downgrade of secure connections to legacy encryption.”

The update will be available with the future specification revision until that Bluetooth SIG is recommending the reduction of the encryption key length below 7 octets is not permitted.

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