New Malware Replaced Legit Android Apps With Fake Ones On 25 Million Devices

Are you sure the WhatsApp app you are using on your Android device is legitimate, even if it's working perfectly as intended?

...Or the JioTV, AppLock, HotStar, Flipkart, Opera Mini or Truecaller app—if you have installed any of these?

I'm asking this because cybersecurity researchers just yesterday revealed eye-opening details about a widespread Android malware campaign wherein attackers silently replaced installed legitimate apps with their malicious versions on nearly 25 million mobile phones.

Now the important question here is how they're doing it and why?

According to researchers at Check Point, attackers are distributing a new kind of Android malware that disguises itself as innocent-looking photo editing, adult entertainment, or gaming apps and available through widely used third-party app stores.

Dubbed Agent Smith, the malware takes advantage of multiple Android vulnerabilities, such as the Janus flaw and the Man-in-the-Disk flaw, and injects malicious code into the APK files of targeted apps installed on a compromised device and then automatically re-install/updates them without the victims' knowledge or interaction.

"It's not enough for this malware family to swap just one innocent application with an infected double. It does so for each and every app on the device as long as the package names are on its prey list," the researchers wrote in their report published Wednesday.

"Over time, this campaign will also infect the same device, repeatedly, with the latest malicious patches. This leads us to estimate there to be over 2.8 billion infections in total, on around 25 Million unique devices, meaning that on average, each victim would have suffered roughly 112 swaps of innocent applications."

The malware, which researchers believe is tied to a China-based firm, has been designed for financial gain by serving malicious advertisements to victims.

How Does Agent Smith Malware Work?

Upon installation of boobytrapped apps, the Agent Smith malware leverages a three-stage infection chain and contains different modules for each step, working of which are explained below:

1.) Loader Module — The initial app distributing the malware contains a module called Loader, whose only purpose is to decrypt, extract, and run the second stage module named Core.

2.) Core Module — Once executed, the Core module communicates with the attackers' C&C server to receive a list of popular apps that needs to be targeted.

If it finds a match installed on the victim's device, the Core module tries to infect the targeted APK using the Janus vulnerability or by simply recompiling the APK with a malicious payload.

Further, to automatically install the modified APK and replace its original version without users' consent, attackers utilize a series of 1-day vulnerabilities, including man-in-the-disk attack.

3.) Boot Module — This module is included in the malicious payload that was bundled with the original app and worked the same as the Loader module. It extracts and executes a malicious payload, called the Patch module when a victim runs the modified application.4.) Patch Module — The patch module has been designed to prevent modified applications from getting legitimate updates, which if installed, would revert all malicious changes.

"While investing a lot of resources in the development of this malware, the actor behind Agent Smith does not want a real update to remove all of the changes made, so here is where the Patch module comes in to play"

"With the sole purpose of disabling automatic updates for the infected application, this module observes the update directory for the original application and removes the file once it appears."

6.) AdSDK Module — This is the actual payload that displays ads to the victims for financial gain and further also infects the device with other adware families.

However, the researchers warn that this modular malware could be easily adapted for far more intrusive and harmful purposes, such as stealing sensitive information—from private messages to banking credentials and much more.

Researchers initially encountered the Agent Smith malware in early 2019, which was primarily being found targeting Android devices in India (with 15 million infected devices) and other nearby Asian countries like Pakistan, Bangladesh, Indonesia, and Nepal.