Posted on August 17, 2019 at 3:28 AM
For users that rely on connectivity resources, it’s not enough that the Internet comes with a long list of security vulnerabilities. As it turns out, Bluetooth can also represent a high risk, as it has possible exploits that can leave users exposed to attacks.
According to security researchers specialized on the matter, there is a new exploit in Bluetooth’s authentication protocols. If the attacker manages to execute correctly, it could take advantage of this vulnerability and perform a man in the middle attack between two devices that have been paired.
A Man In The Middle Attack
A man in the middle attack is that in which the offender puts itself between two different parties and manages to modify the communications between them. The attacker secretly relays any interchange and can even intercept relevant messages, altering them or injecting new ones.
The researchers state that the attacker can intercept and change files that have been shared between two paired devices via the Bluetooth technology. It can also listen to conversations and spy on messages, plus many other things.
This attack has been called KNOB, which means the Key Negotiation of Bluetooth. It was discovered an announced to the world by specialists from several research centers and institutions, including the Oxford University, the Singapore University of Technology and Design, and the CISPA Helmholtz Center for Information Security.
The KNOB Attack, Explained
There is a whole website dedicated to the KNOB attack, which is http://knobattack.com. In a KNOB attack, an agent disguises the entities taking part in a Bluetooth handshake to implement a degraded encryption key, with only one byte of entropy. The situation will pave the way for a simple brute force attack in which the hacker or malicious agent will be able to guess the encryption key in a rudimentary way.
Matthew Green went to his personal Twitter account (@matthew_d_green) to explain the offense and wrote that Bluetooth specs allow one side of the pairing key exchange to suggest a key length in bytes, with no authentication process. The attacker can then manage to push the key size down to 1 byte.
After doing this, the malicious agent will have the freedom to do practically whatever it wants, from spying on the content or changing to injecting its own files into the transfer, among other scenarios that can compromise the integrity of the paired devices and the data being exchanged.
The real danger of the KNOB attack is that it does not precisely constitute a violation of the Bluetooth DR/EDR specification, one that allows keys with only one byte of entropy. The vulnerability works on Bluetooth radios from all prominent brands, including Apple, Intel, and Broadcom.
The attack can be devastating because the victims can’t know that they have been compromised, as the research team conveniently points out. That happens because the events take place at the key exchange process and not in the involved devices.
Light at the End of the Tunnel
However, and despite the evidently devastating consequences of the KNOB attack, there is some light at the end of the tunnel. The Bluetooth SIG recently updated the specifications in order to recommend those that produce regular devices using at least seven bytes of entropy. Another positive development is that manufacturers and brands have been aware of this vulnerability since the final part of 2018 and some of them have developed patches as a protection measure.
And, since it is very difficult to exploit, the odds of it being used in a widespread attack are very low. And for it to be successful, the attacking device needs to be within wireless range of the two devices that are pairing via Bluetooth.
Another potential obstacle for attackers is that if one of the devices does not have the vulnerability, then the attack would be unsuccessful. There are several things that need to happen for a KNOB offense to happen: the device perpetrating it would need to intercept, handle, and retransmit key length negotiation messages between the two paired devices and, additionally, block transmissions from both of them, in a very small window of time.