Apple

iPhone’s AirDrop Bug Exploits Phone Numbers And Emails

AirDrop

If you are an Apple user, then you should be familiar with AirDrop. But if not, here is a brief introduction of this amazing feature. Apple’s AirDrop is supported by all models running on iOS, iPadOS and macOS. Thus, all Apple users have access to it. It allows users to wirelessly share and receive various types of files, such as photos, documents, website, videos, notes, map locations and so on. Generally talking, it’s not the only feature on the market that allows users to share different files with each other. In many aspects, it’s identical to Google’s Nearby Share, which does the same for Android users.

How Does Airdrop Work?

Initially, AirDrop uses Bluetooth to establish a Wi-Fi connection between two Apple devices. And there is no difference what Apple devices are paired iPhone and iPhone, iPhone and Mac, Mac and iPad, etc.

AirDrop

Both devices should have Bluetooth and WiFi turned on and be on a distance of up to 9 meters. Once you select the sharing icon on a file or photo, you will see the nearby devices automatically. So you only have to tap on the receiver to share files with them. However, they can either accept or reject sharing.

Everything sounds quite attractive as Apple offers a quick and easy way to share files with other Apple users even if they are not in your contacts. But is it safe?

1.5 Billion Apple Users Are Vulnerable

Researchers at the Department of Computer Science show that a stranger can see your phone number and email address using a serious bug in AirDrop. In fact, they have found the bug back in 2019. But till the date, the Cupertino company hasn’t fixed it. Moreover, if previously, only partial phone numbers were revealed, now, any time anyone can obtain all information once opens a share sheet.

AirDrop’s Mechanism Has A Backdoor

Important information is typically shared with people we already know. Apple’s AirDrop takes this logic into consideration as well. So it shows receiver devices from address book contacts by default. However, to understand whether the other party is a contact, Apple has developed a mutual authentication mechanism for AirDrop. The mechanism compares a user’s phone number and email address with entries in the other user’s address book.

To better understand this mechanism, a team of researchers from the Secure Mobile Networking Lab (SEEMOO) and the Cryptography and Privacy Engineering Group (ENCRYPTO) at TU Darmstadt conducted research. Not surprisingly for them, they found a severe privacy leak.

Two Issues In AirDrop That Leak Data

It turns out there are two aspects that makes the leak possible:

  1. To make it possible sending files to Contacts only, AirDrop has to request personal data from all devices within range. This is what we talked about above. AirDrop gets and compares a user’s phone number and email address with entries in the other user’s address book.
  2. Of course, the process is encrypted. But Apple uses a relatively weak hashing mechanism. As the researchers from TU Darmstadt showed, ‘hashing fails to provide privacy-preserving contact discovery as so-called hash values can be quickly reversed using simple techniques such as brute-force attacks’.

As a result, anyone can view phone numbers and email addresses of AirDrop users. They only should have a WiFi-capable device and physical proximity to a target that initiates the discovery process by opening the sharing pane.

Is There A Solution?

The same research team has also developed a solution. It’s called ‘PrivateDrop’. The latter is based on optimized cryptographic private set intersection protocols. The team proves the method they suggest determines whether the other party is contact or not without exchanging vulnerable hash values. But it seems Apple doesn’t hurry to use it or solve the problem itself.

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