MacKeeper's developers acknowledged the recently discovered problem and released a fix for it Friday, saying in a blog post that users should run MacKeeper Update Tracker and install version 3.4.1 or later.
MacKeeper registers itself as the handler for a custom URL scheme, allowing websites to automatically call the application through the browser.
Researcher Braden Thomas found an issue in the program's validation of such URLs that makes it possible for attackers to execute arbitrary commands with root privilege when MacKeeper users visit a specially crafted website in Safari. As a proof of concept, he posted a link on Twitter that automatically executes a command to remove MacKeeper when clicked.
If users have already been asked by MacKeeper for their password during the normal operation of the program, the rogue command will execute automatically. If not, the program will prompt them for their password, but the text on the dialog window can also be altered by the exploit, SecureMac reported.
MacKeeper has been surrounded by controversy for years. Its previous owner, a Ukrainian-based company called ZeoBIT, was accused by Mac users of using aggressive advertising and scare tactics to push its product.
The company is close to settling a class-action lawsuit in the U.S. that sought $5 million in damages because MacKeeper warned users about fake security and performance problems to convince them to pay for the full version. If the settlement is reached, ZeoBIT will put $2 million into a fund for refunds, but won't admit any fault.
In April 2013, ZeoBIT sold MacKeeper to another company called Kromtech Alliance. The program has been downloaded over 20 million times and recently celebrated its fifth anniversary, according to Kromtech.