New digitally signed Mac malware confuses users with right-to-left file name tricks

The malware is digitally signed and is probably used in targeted attacks, researchers from F-Secure said

By Lucian Constantin, IDG News Service |  Security

A new piece of digitally signed spyware for Mac OS X uses a special Unicode character in its file name to hide its real file extension from users and trick them into installing it.

The malware, which has been dubbed Janicab.A, is written in Python and is packaged as a stand-alone Mac application using the py2app utility, researchers from security firm F-Secure said Monday in a blog post.

It is distributed as a file called "RecentNews.?fdp.app" where the "?" is actually the right-to-left override (RLO) character known as U+202E in the Unicode encoding standard.

Unicode supports characters from most languages, including those written from right to left like Arabic and Hebrew. The special RLO character tells software that the text following it should be displayed from right to left.

Apple displays double extensions for security reasons in the Mac OS X file manager, said Sean Sullivan, a security advisor at F-Secure, Tuesday via email. "Here, the RLO trick is being used to counter that and to make the .app appear to be a .pdf."

The trick itself is not new and has been used by Windows malware in the past, including by the Bredolab email spam malware and the Mahdi cyberespionage Trojan program that targeted computers in the Middle East.

Opening the Janicab .app file will trigger a standard Mac OS X pop-up dialog warning the user that the file was downloaded from the Internet. However, because of the RLO character in the file name, the entire warning text will be written right to left making it confusing and hard to read.

If users agree to open the file, the malware will install itself in a hidden folder in the user's home directory and will open a decoy PDF document containing what appears to be a news article in Russian.

Janicab continuously takes screenshots and records audio and uploads the collected data to command and control (C&C) servers that it finds by parsing the description of specific YouTube videos. It also queries the C&C servers for commands to execute, the F-Secure researchers said in the blog post.

Based on statistics for the YouTube videos whose descriptions are parsed by the malware, the malware's functionality and the contents of the decoy document, F-Secure researchers believe the malware is being used in targeted attacks, Sullivan said. However, the company doesn't have any information about the identity of the targets, he said.

Janicab samples were uploaded to the VirusTotal malware scanning service from five countries, but that information might reflect the locations of different security researchers, not victims, Sullivan said.

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