Android Malware Actively Infecting Devices to Take Full Control

Android malware infects devices to take full control for various illicit purposes like:- 

• Stealing sensitive information
• Generating unauthorized financial transactions
• Enabling remote attacks

By gaining complete control, threat actors can exploit the device for their illicit activities, posing significant threats to:-

• User privacy
• User security

Cybersecurity analysts at McAfee Mobile Research recently found an Android backdoor, “Android/Xamalicious,” using the Xamarin framework to infect devices and take full control.

Android Malware Gain Device Control

It employs social engineering for accessibility privileges and communicates with the C2 server. Second-stage payload dynamically injected as assembly DLL, which takes full control for:-

• Ad fraud
• App installs
• Financially motivated actions

Researchers identified the link to the ad-fraud app “Cash Magnet,” revealing financial motivation. Xamarin usage allows long-term activity, hiding malicious code in the APK build process. 

The custom encryption and the obfuscation techniques were used for communication and data exfiltration. Around 25 malicious apps carry the threat, some on Google Play since mid-2020. 

McAfee’s proactive measures and Google Play Protect aim to mitigate Potentially Harmful Applications. Android/Xamalicious detected on at least 327,000 devices, remains highly active.

Android/Xamalicious trojans disguise as apps from the following categories that are available in third-party markets:-

• Health
• Game
• Horoscope
• Productivity

Unlike previous Xamarin-based malware, Xamalicious is distinct in its implementation. Xamarin architecture allows .NET code interpretation on Android via Mono. 

An example app, “Numerology” prompts victims to enable accessibility services for deceptive functionality.

All the accessibility services need to be activated manually after several OS warnings.

Malware varies from traditional Java or ELF Android code and the original .NET, compiled into DLL, LZ4 compressed, and embedded in BLOB or /assemblies directory.

Besides this, it is loaded by ELF or DEX at runtime, reversing varies in complexity, and the code is commonly available in the following assemblies:- 

• core.dll
• <package-specific>.dll

Some variants obfuscate DLLs, while others retain the original code. After acquiring accessibility permissions, the malware contacts the server for the second-stage payload.

Xamalicious malware checks the victim’s device info, like apps and rooting status, via system commands. If rooted or connected via ADB, it skips the second-stage payload download.

Here below, we have mentioned the types of information that are collected by the malware:-

With the help of RSA-OAEP and HTTPS, the Xamalicious encrypts all the data to evade detection. However, if the C2 infrastructure is available, then the hardcoded RSA keys in the DLL enable decryption. 

The Send() function encrypts data with a JWT and sends it to “/Updater” via HTTP POST. The decrypt() function uses a hardcoded RSA private key for C2 responses, possibly containing a second-stage payload.

Data sent to the C&C server that decides second-stage payload delivery and malware’s self-protection includes:- 

• Rooting
• ADB
• SIM checks

The C&C encrypts DLL with AES and device-specific key, the device decrypts the token, and then the ‘URL,’ parameter with a custom AES key unique to device details.

Malicious apps Detected

Here below, we have mentioned all the malicious apps detected:-

Countries from where users were affected

Here below, we have mentioned all the countries from where most of the users are affected:-

• The USA
• Brazil
• Argentina
• The UK
• Spain
• Germany

IOCs