SecureMac Issues Critical Security Advisory for MacKeeper Users

Stephen Yagielowicz

LOS ANGELES — Apple Macintosh and Mac OS X security specialists SecureMac, has issued a critical security advisory for users of the OS X utility program MacKeeper.

According to SecureMac, a flaw in MacKeeper’s URL handler implementation allows arbitrary remote code execution when a user visits a specially crafted webpage. MacKeeper was originally created by Ukrainian company ZeoBIT, and is now distributed by Kromtech Alliance Corp.

Security researcher Braden Thomas discovered the flaw, caused by MacKeeper’s lack of input validation when executing commands using its custom URL scheme, enabling commands to be run as “root” with little to no user interaction required.

Thomas published a proof-of-concept (POC) that demonstrates how using Safari to visit a specially coded webpage causes the affected system to execute various commands, which in the case of the POC, will uninstall MacKeeper.

SecureMac notes that while the POC is relatively benign, the source code provided with it could easily be modified to perform malicious attacks.

“If MacKeeper has already prompted the user for their password during the normal course of the program’s operation, the user will not be prompted for their password prior to the arbitrary command being executed as root,” explains a SecureMac spokesperson. “If the user hasn’t previously authenticated, they will be prompted to enter their username and password — however, the text that appears for the authentication dialog can be manipulated as part of the exploit and set to anything, so the user might not realize the consequences of this action.”

As with other operating systems, Apple allows OS X and iOS apps to define custom URL schemes and register them with the operating system so that other programs know which app should handle the custom URL scheme.

“Normally, this is used to define a custom communication protocol for sending data or performing a specific action (for example, clicking a telephone number link in iOS will ask if the user wants to dial that number, or clicking an email address link in OS X will open and compose a new message to that person),” the spokesperson adds. “Apple’s inter-application programming guide explicitly tells developers to validate the input received from these custom URLs in order to avoid problems related to URL handling. Additionally, Apple has provided information on the importance of input validation in their Secure Coding Guide.”

It appears that these security guidelines were ignored.

According to MacKeeper, its software has surpassed 20 million downloads worldwide, but despite this popularity, reports from users have cited its numerous pop-ups and advertisements as major negatives, and it remains to be seen how this latest revelation will affect its users.

A workaround is available for MacKeeper users until this vulnerability in the program is fixed: On OS X, clicking a link in Safari that uses a custom URL scheme will automatically open the program that is registered to handle that type of URL. Other browsers, such as Google’s Chrome, will ask the user for permission before opening a link that uses an external protocol. Non-technical users could use a web browser other than Safari, in order to see an alert before a link could cause an arbitrary command to be executed, while more technical users could remove the custom URL scheme handler from MacKeeper’s Info.plist file.

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