CVE-2020-26557

A flaw was found in the Linux kernel’s Bluetooth Mesh Profile implementation. The Mesh Provisioning procedure has a vulnerability that allows an attacker observing or taking part in the provisioning to brute force the AuthValue if it has a fixed value or is selected predictably or with low entropy. If successful, an attacker can identify the AuthValue and authenticate to both the Provisioner and provisioned devices, allowing a Man-in-the-Middle (MITM) attack on a future provisioning attempt with the same AuthValue. The highest threat from this vulnerability is to confidentiality, integrity, as well as system availability.

Mitigation

It is recommended for devices to use AuthValues containing the maximum entropy permitted (128-bits) and randomly select a new AuthValue using a secure random number generator with each new provisioning attempt. A large entropy helps ensure that a brute-force of the AuthValue, even a static AuthValue, cannot normally be completed in a reasonable time.