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AirDrop, feature that allows Mac and iPhone users can transfer files wirelessly between devices, filter users ’emails and phone numbers, and no one can do anything but turn them off, the researchers said.
AirDrop uses Wi-Fi and Bluetooth Low Energy to establish direct connections with nearby devices so you can send photos, documents, and more iOS or macOS the device to another. One mode allows you to connect only to contacts, the second allows you to connect to anyone, and the last does not allow any connection.
To determine whether the device of an AirDrop transmitter should connect to other nearby devices Bluetooth advertisements with a partial cryptographic hash of the sender’s phone number and email address. If there is a starter that has been hacked with any phone number or email address in the recipient’s address book, or if the device is set to receive from everyone, the two devices will perform a Wi-Fi mutual authentication intervention. When you shake hands, the devices exchange the full hash of SHA-256 phone numbers and email addresses of the owners.
Hashes, of course, cannot be converted to clear text that he re-created, but depending on the entropy or random number in the clear text, they can often be guessed. Hackers do this by carrying out a “brute force attack” that throws out a lot of inventions and waits for the one who creates the requested hash. The less entropy in the clear text, the easier it is to guess or crack, because there are fewer candidates to test an attacker.
The number of entropies in a phone number is so small that this cracking process is insignificant, as it takes milliseconds to search for a hash in a pre-calculated database that collects the results of all possible phone numbers in the world. Although many email addresses have a higher entropy, they can also be broken down by using the billions of email addresses that have appeared in database breaches over the past 20 years.
“This is an important finding because attackers allow Apple users to obtain relatively personal information, then take steps to carry out spear attacks, scams, etc., or simply sell them,” said one of the researchers, Christian Weinert. he found weaknesses at the Technical University of Darmstadt, Germany. “Who doesn’t want to send a message directly, say, Donald Trump on WhatsApp? All attackers need a Wi-Fi-enabled device next to the victim.”
In one paper presented at the USENIX Security Symposium in August, Weinert and researchers at the SEEMOO laboratory in TU Darmstadt devised two ways to exploit vulnerabilities.
The easiest and most powerful method is to control the discovery requests that an attacker sends to other nearby devices. As the sender’s device shows its initial phone number and email address, each time it crawls the available AirDrop receivers, the attacker must wait for a nearby Mac share menu or nearby iOS devices share page. The attacker does not have to have a phone number, email address or any other knowledge about the target.
A second method works in reverse to a large extent. An attacker can open a share menu or share page and see if nearby devices are responding with their hashe details. This technique is not as powerful as the first, as it only works if the attacker’s phone number or email address is in the recipient’s address book.
However, the attack could be useful when the attacker is someone whose phone number or email address is known to many people. A manager, for example, could use the manager’s contact information to get the phone number or email address of employees stored in address books.
Weinert wrote in an email:
What we call “sender leaks” (i.e., someone intending to share a file escapes their hash contact identifiers) could be exploited by planting “bugs” (small Wi-Fi-enabled devices) in public places or other places of interest.
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