iMessage URL Preview Exposes User Data

Apple’s iMessage service can leak data such as location, device type, and operating system, when the user receives a URL in a message, a researcher has discovered.

The issue, researcher Ross McKillop explains, resides in a new feature in iMessage, which allows the service to extract some metadata from the URL and display it as a clickable link. The feature is available on both MacOS and iOS and behaves in a similar manner.

The feature, McKillop reveals, was supposed to work in a manner similar to that used by services such as Facebook or Slack, but it doesn’t. Although it does provide meaningful content for a link, the iMessage implementation sends requests from the device itself, and not from the service, as it happens with Facebook and Slack.

Thus, when iMessage requests the data from the website, it shares information such as the receiver’s IP address, device type, and OS version. With the service available on multiple Apple devices, including iPad, iPhone, Mac, both MacOS and iOS users are impacted by the vulnerability, the researcher says.

What’s more, he says, the request is sent from each of the devices the receiver has, meaning that an attacker sending an URL can determine if the potential victim is at home (based on the IP addresses the victim’s Mac and iPhone send back), or the victim’s physical location (if the IP of a foreign mobile network appears in the request).

The issue could have deeper implications, McKillop suggests: “As this request is clearly being made, and parsed, by Safari from the User-Agent string it’s reasonable to believe that there is potential that an exploit found in Safari could be triggered without the target even browsing to the site, simply by sending them an iMessage containing that URL.”

Another issue is that the user cannot switch off the automatic request behavior, though Apple might consider a remedy for the bug in an upcoming update. One solution, McKillop says, is to “extract the metadata on the sending device (they obviously trust the URL) and encapsulate that as metadata within the message.”

Recently, Apple’s iMessage service was found to send information about a user’s contacts to Apple servers. Although the service’s end-to-end encryption would make conversations private, Apple’s servers received details on who a user might have contacted over iMessage, along with their date and time, and IP address. Apple admitted that it was sharing this information with law enforcement agencies when required to.

Related: Apple Patches Serious Encryption Flaws in iMessage