Malvertising campaign targets Apple users with malicious code hidden in images

Apple users continue to be some of the favorite targets of malvertising campaigns, according to a report published this week by cyber-security firm Confiant.

The report describes a new malvertising group called VeryMal that's been going after Apple users, with the latest campaigns employing steganography techniques to hide malicious code inside ad images to avoid detection.

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The Confiant report comes after the company discovered a different malvertising group last year, named ScamClub, which also exclusively targeted Apple users.

But while ScamClub was a much bigger operation, hijacking as many as 300 million web sessions for US-based iOS users, the VeryMal group is a much smaller in size, being blamed for only five million hijacks.

However, the difference, according to researchers, is that this newer group is way sneakier, employing steganography to hide the code responsible for redirecting users from legitimate sites to malicious ones.

According to Confiant's recent report, this is how the most recent VeryMal malvertising effort unfolded:

1. Ad slot on a legitimate website loads an image
2. The image contains code hidden inside some of its pixel data values
3. The ad slot also loads additional JavaScript code
4. The JS code checks to see if Apple fonts are supported.
5. If it's an Apple device, this JavaScript code reads the image file to extract the hidden code from inside it.
6. The external JavaScript code executes the code extracted from the image.
7. This extracted code is a JavaScript command that forces the browser to navigate to a new URL.
8. The user is bounced around through different subsequent URLs until he lands on a page showing popups urging him to install software updates --usually for Adobe Flash Player.

Confiant says it's been tracking this group and its campaigns --which usually run in short bursts for a few days-- since August last year. Collectively, the VeryMal group appears to have hijacked over 5 million web sessions from legitimate sites, however, it is unknown how many of the users installed the malware-laced apps.

According to Malwarebytes, the tainted software updates contained a version of Shlayer, a Mac malware strain that is used as an intermediary before its operators installed various adware strains on infected devices.

More details about the Shlayer malware are available in the Confiant report, but also in an Intego report from February 2018.

Confiant says that the VeryMal group didn't always use steganography to hide its malvertising operation, this being a recent addition to the campaigns set in motion this month.

While the January campaign targeted Mac users, Confiant said that in the past VeryMal operators also went after iOS users in previous campaigns.

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Similarly to the ScamClub group, VeryMal also targeted US users exclusively in some of its campaigns.

According to a GeoEdge report published last November, malicious code hidden inside ad images caused financial losses to ad networks estimated at around $1.13 billion in 2018 alone.

Steganography is becoming a very common technique that malware groups use these days to hide malicious code inside images. A report published by EdgeSpot yesterday also detailed how another group hid the exploit code for an Adobe Reader vulnerability inside images, to avoid security scanners for detecting it.

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