Malicious Android apps posing as file managers have been identified and removed from the Google Play Store recently after infecting tens of thousands of users with a SharkBot banking trojan. This is not the only time the Google Play Store has been in the news recently for distributing malicious apps of different types. At the end of October and beginning of November, 20 different apps were reportedly on the Google Play Store that were trojans for clicker malware or opened phishing links through pop-up adware, which affected over 20 million users. In August of this year, an additional 35 apps sharing malicious ads and performing obfuscation techniques to hide on the device after download were identified and removed after over 2 million users were affected.  

Threat researchers have reported on an Android banking trojan known as SharkBot since October 2021. This initial discovery included a botnet that was targeting the UK, Italy, and US-based users. The most recent apps found with the SharkBot malware were also found to preferentially target users in the UK and Italy, with over 80% of the malware samples identified being found in the UK, and the next highest concentration was 16% in Italy. Researchers at Bitdefender performed a code analysis on the recent trojan apps, and discovered that anti-emulator checks were performed by the apps to verify the presence of a SIM from Italy or Great Britain by checking the ISO before dropping the malware onto the device. The developer profile for these apps was also only viewable on the Google Play Store when viewed from a UK or Italy-based country code in the browser, again affirming the geographic targeting of these apps. 

One app identified was ‘X-File Manager’, which works by tricking the user into installing the SharkBot malware by disguising it as an update for the already installed X-File Manager app. Since the malware is not present within the original app and is instead dropped onto the device at a later date, the app manages to pass security tests to be listed on the Google Play Store and reach a wide range of victims. The app also needs permissions to be granted by the user, as the disguise of a file manager app makes the requested permissions appear less suspicious. The permissions that are asked to be granted include READ_EXTERNAL_STORAGE, WRITE_EXTERNAL_STORAGE, GET_ACCOUNTS, REQUEST_INSTALL_PACKAGES, QUERY_ALL_PACKAGES, and REQUEST_DELETE_PACKAGES.  

The app then uses these permissions to search the device to identify if it is from a target country, Great Britain or Italy, and to determine if the device also has a banking application installed that is on their list of targets. Threat researchers at Bitdefender and Threat Fabric have published a list of banking apps recent versions of this malware has been found to target, however Bitdefender also warn that this list is not exclusive, as it can be updated remotely by the attackers at any time. The app then sends a request URI to download the malware component. This is via a fake update named ‘_File Manager’, which requires user interaction to complete the dropped APK (Android Package Kit) installation. A fake pop-up update page opens in a browser spoofing the Play store to make this appear like a legitimate update. 

Once the SharkBot malware is on a device, it can be used by the attackers to steal login credentials for online bank accounts. This is performed through fake login pages for target banking apps being displayed by the malware over the top of legitimate login prompts from the banking app that has been spoofed. The attackers use these credentials, as well as a variety of multi-factor authentication bypass techniques to initiate money transfers through ATS (Automatic Transfer Systems). Other apps with similar attack techniques to X-File Manager which were also recently removed from the Google Play Store for being SharkBot trojans include ‘FileVoyager’, ‘Phone AID, Cleaner, Booster’, and ‘LiteCleaner M’. 

Using an official source to obtain apps, such as the Google Play Store, is supposed to ensure that the apps you download are trusted by the distribution company and can therefore be trusted by you, however, this has not been the case with Google Play Store. But, it is still safer to use the official provider, as third party app distribution sites do not have to provide the same level of checks and security that is expected from the official sites. Similar SharkBot trojan banking apps are still easily accessible on third party Android app sites despite being now removed from the Google Play Store, so it is still a greater risk to use these alternative sites to obtain apps.  

Ensuring that you do not download apps that you don’t need, are cautious with the permissions that you grant apps, and delete unused and old apps from your devices, can provide some protection against falling victim to a malicious trojan app. Installing anti-virus software on mobile devices also provides security against these cyber-attacks, such as through the detection of malware and viruses. Scam detection and web browsing protection are often also available through anti-virus software to further increase the security of your device. Deleting a suspicious or malicious app and all its data should remove the presence of malware for the device. The Google Play Store also offers a service called Play Protect which can automatically remove malicious apps from your device when they are removed from the Google Play Store.