A flaw in the mobile Safari browser has been exploited by cybercriminals and used to extort money from individuals who have previously used their mobile device to view pornography or other illegal content. The Safari scareware prevents the user from accessing the Internet on their device by loading a series of pop-up messages.

A popup is displayed advising the user that Safari cannot open the requested page. Clicking on OK to close the message triggers another popup warning. Safari is then locked in an endless loop of popup messages that cannot be closed.

A message is displayed in the background claiming the device has been locked because the user has been discovered to have viewed illegal web content. Some users have reported messages containing Interpol banners, which are intended to make the user think the lock has been put on their phone by law enforcement. The only way of unlocking the device, according to the messages, is to pay a fine.

One of the domains used by the attackers is police-pay.com; however, few users would likely be fooled into thinking the browser lock was implemented by a police department as the fine had to be paid in the form of an iTunes gift card.

Other messages threaten the user with police action if payment is not made. The attackers claim they will send the user’s browsing history and downloaded files to the Metropolitan Police if the ransom is not paid.

This type of Safari scareware is nothing new, although the zero-day flaw that was exploited to display the messages was. The attackers loaded code onto a number of websites which exploited a flaw in the way the Safari browser handles JavaScript pop-up windows. The code targeted iOS versions 10.2 and earlier.

The Safari scareware campaign was recently uncovered by Lookout, which passed details of the exploit onto Apple last month. Apple has now released an update to its browser which prevents the attack from taking place. Users can protect their devices against attack by updating their device to iOS version 10.3.

Scareware is different from ransomware, although both are used to extort money. In the case of ransomware, access to a device is gained by the attacker and malicious file-encrypting malware is downloaded. That malware then locks users’ files with powerful encryption. If a backup of the encrypted files is not owned, the user faces loss of data if they do not pay the attackers for the key to decrypt their locked files.

Scareware may involve malware, although more commonly – as was the case with this Safari scareware campaign – it involves malicious code on websites. The code is run when a user with a vulnerable browser visits an infected webpage. The idea behind scareware is to scare the end user into paying the ransom demand to unlock their device. In contrast to ransomware, which cannot be unlocked without a decryption key, it is usually possible to unlock scareware-locked browsers with a little computer knowhow. In this case, control of the phone could be regained by clearing the Safari cache of all data.