Infected Android app store

The APKPure app store has been infected by a malicious module that downloads Trojans to Android devices.

We always recommend downloading apps from official stores only, to reduce the likelihood of installing malware. However, unofficial stores not only host malicious apps, but they might not be safe at all. Following a recent investigation, we are sorry to report that APKPure, a popular alternative source of Android apps, was Trojanized and has been distributing other Trojans.

What is APKPure for?

The most official of all Android app stores is, of course, Google Play. But it is available only on devices that use Google Mobile Services (GMS) and are firmly tied to Google’s infrastructure. Some vendors avoid GMS libraries to stay independent, and because Android is an open operating system, they can.

For users, there are both advantages and disadvantages. One prominent disadvantage is a loss of access to Google’s app store, where Android users can download the usual apps.

That’s where alternative stores come in, and APKPure is one of them. Distinctively, it hosts only free or shareware apps. Also, the owners stress that the apps in their store have all been scanned by Google and are completely safe; they say their apps are exactly the same as the ones on Google Play.

What happened with APKPure?

The apps in the store may have passed all tests, but the APKPure app hasn’t. This incident smacks strongly of the CamScanner episode, in which the app’s developers implemented an advertisement SDK from an unverified source and it turned out to be malicious. That’s also how malware got into APKPure.

Looks like APKPure version 3.17.18 was likewise fitted with an advertisement SDK, one with an embedded Trojan dropper, which Kaspersky solutions detect as HEUR:Trojan-Dropper.AndroidOS.Triada.ap. When launched, it unpacks and runs its payload, which is the dangerous part. This component can do several things: show ads on the lock screen; open browser tabs; collect information about the device; and, most unpleasant of all, download other malware.

What can happen to a device with APKPure installed?

Which Trojan gets downloaded (in addition to APKPure’s built-in one) depends on the Android version, as well as on how regularly the smartphone vendor released — and the user installed — security updates.

If the user has a relatively recent version of the operating system, meaning Android 8 or higher, which doesn’t hand out root permissions willy-nilly, then it loads additional modules for the Triada Trojan. These modules, among other things, can buy premium subscriptions and download other malware.

If the device is older, running Android 6 or 7, and without security updates installed (or in some cases not even released by the vendor), and thus more easily rootable, it could be the xHelper Trojan. Removing this beast is a real challenge; even a factory reset won’t do it. Armed with root access, xHelper lets attackers do almost anything they want on the device.

Is APKPure safe now?

On April 8, we informed APKPure about the issue. On April 9, APKPure representatives replied that they saw the problem and were working on the fix. Shortly after that, a new version (3.17.19) appeared on the APKPure website. According to its description, the update “Fixed a potential security problem, making APKPure safer to use.”

We can confirm that the problem has indeed been fixed: APKPure 3.17.19 doesn’t contain the malicious component. It is safe to use.

How to guard against Trojanized APKPure

If you don’t use APKPure, then don’t worry — today’s problem does not concern you. But to avoid similar issues in the future:

  • Never download apps from unofficial sources, and block the installation of apps from third-party sources in Android’s settings;
  • Use a reliable security solution that automatically scans all new files;
  • Regularly update all apps and the operating system.

If you do use APKPure, we additionally recommend that you:

  • Update the APKPure app to the version in which the issue is fixed (that is, 3.17.19 or newer);
  • Run a full antivirus scan of the device.
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