Mac Malware Uses Right-to-Left Override Technique to Disguise Executables

Researchers at F-Secure have spotted a malware attack using a trick commonly associated with Windows malware to go after Mac users.

The attack uses right-to-left override [RLO], a special character used in bi-directional text encoding system to mark the start of text that are to be displayed from right to left, explained Broderick Aquilino, an F-Secure Labs Analyst. RLO is commonly used by Windows malware such as Bredolab and was also used by the high-profile Mahdi Trojan discovered last year as a means of hiding the actual extension of executable files, he blogged.

“[The objective] here it’s simply to hide the real extension,” he continued. “The malware could have just used “Recent New.pdf.app”. However OS X has already considered this and displays the real extension as a precaution.”

According to F-Secure, the malware continuously takes screen shots and records audio before uploading the data to a command and control servers. It also polls the C&C constantly for commands to execute.

“The malware is written in Python and it uses py2app for distribution,” Aquilino blogged. “Just like Hackback, it’s signed with an Apple Developer ID.”

However, because of the RLO character, the usual file quarantine notification from OS X will be backwards, he added. The malware drops and opens a decoy document when it is executed, then creates a cron job for its launch point and a hidden folder in the home directory of the infected user to store its components. To obtain the address of its command and control server, the malware connects to certain YouTube pages and parses for the address in the string “just something i made up for fun, check out my website at (address) bye bye.”

The malware is detected by F-Secure as Backdoor:Python/Janicab.A.