Android SharkBot Droppers on Google Play Underline Platform's Security Needs

A common theme we've noticed in the last few months consists of malicious apps distributed directly from the Google Play Store. If something comes from an official store, people could be inclined to believe it’s safe. Our research has shown this to be false, many times over.

Only a few months ago, Bitdefender found a trove of malicious apps in the official store that pushed aggressive unwanted ads that could lead to more serious attacks.

Thanks to our real-time behavioral technology designed to detect software acting suspiciously, we uncovered apps downloaded from Google Play acting as droppers for SharkBot bankers shortly after installation, depending on the user's location.

The Google Play Store would likely detect a trojan banker uploaded to their repository, so criminals resort to more covert methods. One way is with an app, sometimes legitimate with some of the advertised features, that doubles as a dropper for more insidious malware.

The apps Bitdefender found are disguised as file managers, which explains why they request permission to install external packages (REQUEST_INSTALL_PACKAGES) from the user. Of course, that permission is used to download malware. As Google Play apps only need the functionality of a file manager to install another app and the malicious behavior is activated to a restricted pool of users, they are challenging to detect.

While none of the apps in this research are still available on the Google Play Store, they're still present across the web in different third-party stores, making them a current threat.

Most users who have downloaded the apps are primarily from the United Kingdom and Italy, with a small minority in other countries as well.

X-File Manager

We found the application X-File Manager (com.victorsoftice.llc) from Google Play that had more than 10,000 installs before it was deleted.

• https://play.google[.]com/store/apps/details?id=com.victorsoftice.llc&hl=EN

The application installs a SharkBot sample with the label _File Manager, and the user is tricked into thinking that an update to the app must be installed.

The developer profile on Google Play seems to be visible only to users from Italy and Great Britain. Accessing its page without specifying the country code is not possible.

Multiple users claim that the application drops malware, and the target of the criminals becomes apparent as the negative reviews for the apps are all in Italian.

When we took a closer look at the X-File Manager app we found the sample has multiple permissions expected of a file manager, including READ_EXTERNAL_STORAGE, WRITE_EXTERNAL_STORAGE, GET_ACCOUNTS, REQUEST_INSTALL_PACKAGES, QUERY_ALL_PACKAGES, REQUEST_DELETE_PACKAGES.

Upon code analysis, we discovered the application performs anti-emulator checks and targets users from Great Britain and Italy by verifying if the SIM ISO corresponds with IT or GB. It also checks if the users have installed at least one of the targeted banking applications on their devices.

Searching for the targeted bank:

The encryption of the country codes, URL, banking list was also found in this sample:

Here’s a list of apps monitored by the malware that includes other financial services. It’s worth noting that this is not a fixed list as the attackers can always add support for new apps.

The URL redirects to a Russian Federation IP:

• http://94[.]198[.]53[.]205/loader_08_2022_03e19619736ebb206d5dc24b6ca3a84f/

The application performs a request at URI, downloads the package, and writes the malicious payload on the device. The dropper fakes an update of the current application to complete the installation and asks the user to install the dropped APK.

While the app is no longer available on the Google Play Store, it’s still on other websites:

• https://apksos[.]com/app/com.victorsoftice.llc
• https://pt.modapkdown[.]com/com.victorsoftice.llc/x-file-manager-mod/

Other similar sample found on Google Play

FileVoyager is also a file manager following the same pattern.

• https://play.google[.]com/store/apps/details?id=com.potsepko9.FileManagerApp

Users also claim that the application is suspicious and even malware.

The same encrypted list containing country codes, URL, and banks can be found in com.victorsoftice.llc.

We also found a similar sample named 'Phone AID, Cleaner, Booster' available on the web through third-party app stores:

• https://apksos[.]com/app/com.sidalistudio.developer.app
• https://apkaio[.]com/app/com.sidalistudio.developer.app
• https://www.modapkdown[.]com/com.sidalistudio.developer.app/phone-aid-cleaner-booster-mod/

'LiteCleaner M' is yet another Sharkbot sample that was published on Google Play then deleted, but not before being downloaded by over 1,000 people. It is still present on various third-party online websites.

• https://apksos[.]com/app/com.ltdevelopergroups.litecleaner.m

SharkBot Droppers packages and Indicators of Compromise:

IOCs:

The SharkBot sample is detected as Android.Trojan.Banker.ZP