New Tekya Ad Fraud Found on Google Play
We observed a Tekya variant that had made its way onto Google Play via five malicious apps. Said apps were already removed from the Play Store.
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In late March, researchers from CheckPoint found the Tekya malware family, which was being used to carry out ad fraud, on Google Play. These apps have since been removed from the store, but we recently found a variant of this family that had made its way onto Google Play via five malicious apps, although these have also been removed. (We detect these as AndroidOS_Tekya.HRX.)
Figures 1 and 2. Apps with Tekya malware (Click to enlarge)
Connections between two versions
This variant of Tekya shares many similarities with the previously found version. For example, the encryption remains essentially identical. The same algorithms and keys are used in both versions.
Figure 3. Encryption code from previous Tekya version
Figure 4. Encryption code from this Tekya version
How this Tekya variant works
The malware registered a receiver that responds to the actions “com.tenjin.RECEIVE” or “android.intent.action.BOOT_COMPLETED”. The latter action gives the malware the ability to wake after the device boots:
Figure 5. Registered receiver
The functionality of the receiver is implemented in libtenjin.so. Once called, it would then call a method which hides itself in a common package — specifically, com/google/android/gms/internal/ads/.
Figure 6. Malicious method call
The method called is responsible for downloading a .dex file and loading it. In the case we were analyzing, the said file would be downloaded twelve hours after the malware was installed. The downloaded file is encrypted; it is decrypted and loaded by libtenjin.so.
Figure 7. Decryption and loading of decrypted file
Once the downloaded .dex file been loaded, it would attempt to register itself with a configuration server. The information that is part of the registration includes device ID, user accounts, location, MAC address, and others (as seen below):
If the server did not reject the registration, an encrypted configuration file would be downloaded. This contains information about the ads to be loaded and control flags. (The blurred text contains information about about the ad accounts potentially used by the attacker, which we have opted to remove.)
Figure 9. Contents of downloaded configuration file
The malware would do various checks, including time, control flags, and so on based on the downloaded configuration. If those checks passed, Tekya would hide itself.
According to its code, Tekya would target up to 11 advertising networks, including: Admob, Facebook, and Unity. Advertisements from these networks would be displayed, and user touch events imitated through InputManager.
Figure 11. Code to load Admob
Figure 12. Code to inject input event
Tekya would try to trick victims into believing those advertisements were opened by other applications by changing its icon and label to that of another app on the device.
Figure 13. Code for Tekya to choose which icon and label to imitate
We originally found several of these apps on Google Play, but Google removed these from the App Store while our research was underway. We are still watching for any similar threats that may emerge in the wild.
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Indicators of Compromise (IOCs)
All of the malicious files below are detected as AndroidOS_Tekya.HRX.