Mac Backdoor in Disguise

Monday, December 11, 2017 @ 07:12 PM gHale

As Apple products become more popular and usage continues to climb in the manufacturing automation sector, users need to remain aware of various attacks hitting the operating system.

One such attack, OceanLotus, is a backdoor using a technique to disguise the fact it is an executable, researchers said.

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HiddenLotus, a variant of the OceanLotus backdoor, is a backdoor distributed via an application named Lê Thu Hà (HAEDC).pdf, which it pretends to be an Adobe Acrobat file, said researchers at Malwarebytes.

The app uses a method that inspired the file quarantine feature introduced in Leopard (Mac OS X 10.5), where files downloaded from the Internet are tagged as quarantined.

Should the downloaded file be an executable, such as an application, a pop-up notification warns the user when they attempt to open the file. The quarantine feature has been around for nearly a decade, but malware continues to masquerade as documents, Malwarebytes researchers said in a post.

HiddenLotus was last seen going out looking like a Microsoft Word document and targeting users in Vietnam. While older malware had a hidden .app extension to indicate it was an application, HiddenLotus has a .pdf extension. There was no .app extension included.

At the end of last month, Apple added a signature to the macOS XProtect anti-malware system for OSX.HiddenLotus.A.

“An application does not need to have a .app extension to be treated like an application. An application on macOS is actually a folder with a special internal structure called a bundle. A folder with the right structure is still only a folder, but if you give it an .app extension, it instantly becomes an application,” Malwarebytes researchers said.

Because of that, the Finder treats the folder as a single file and launches it as an application when double-clicked, instead of opening the folder.

When the user double-clicks a file or a folder, LaunchServices considers the extension first and opens the item accordingly, if it knows the extension. A file with a .txt extension will be opened with TextEdit by default. Thus, a folder with the .app extension will be launched as an application, should it have the right internal structure.

If the extension isn’t known, the user is consulted when attempting to open the file, and they can choose an application to open the file or search the Mac App Store.

When double-clicking a folder with an unknown extension, however, LaunchServices falls back on looking at the folder’s bundle structure.



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