Google Play apps steal texts and pepper you with unauthorized purchases

April 20, 2021 by No Comments

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Security researchers have uncovered a batch of Google Play apps that stole users’ text messages and made unauthorized purchases on users’ dimes.

The malware, which was hidden in eight apps that had more than 700,000 downloads, hijacked SMS message notifications and then made unauthorized purchases, McAfee mobile researchers Sang Ryol Ryu and Chanung Pak said Monday. McAfee is calling the malware Android/Etinu.

User data free for the taking

The researchers said an investigation of the attacker-operated server that controlled infected devices showed it stored all kinds of data from users’ phones, including mobile carrier, phone number, SMS messages, IP address, country, and network status. The server also stored auto-renewing subscriptions, some of which looked like this:

No joke

The malware is reminiscent, if not identical, to a prolific family of Android malware known as Joker, which also steals SMS messages and signs up users for pricey services.

“The malware hijacks the Notification Listener to steal incoming SMS messages like Android Joker malware does, without the SMS read permission,” the researchers wrote, referring to Etinu. “Like a chain system, the malware then passes the notification object to the final stage. When the notification has arisen from the default SMS package, the message is finally sent out using WebView JavaScript Interface.”

While the researchers say that Etinu is a malware family distinct from Joker, security software from Microsoft, Sophos, and other companies use the word “Joker” in their detection names of some of the newly discovered malicious apps. Etinu’s decryption flow and use of multi-stage payloads are also similar.

The decryption flow.

The decryption flow.

McAfee

In an email, McAfee’s Sang Ryol Ryu wrote, “While Etinu looks very similar to Joker, in-depth, its processes for loading payloads, encryption, targeting geographies are different from Joker.”

The Etinu payloads appear in an Android Assets folder with file names such as “cache.bin,” “settings.bin,” “data.droid,” or “image files.”

McAfee

Multi stage

As depicted in the decryption flow diagram above, hidden malicious code in the main installation file downloaded from Play opens an encrypted file named “1.png” and decrypts it using a key that’s the same as the package name. The resulting file, “loader.dex” is then executed, resulting in an HTTP POST request to the C2 server.

“Interestingly, this malware uses key management servers,” the McAfee researchers wrote. “It requests keys from the servers for the AES encrypted second payload, ‘2.png.’ And the server returns the key as the ‘s’ value of JSON. Also, this malware has self-update function. When the server responds ‘URL’ value, the content in the URL is used instead of ‘2.png’. However, servers do not always respond to the request or return the secret key.”

McAfee

The apps and corresponding cryptographic hashes are:

08C4F705D5A7C9DC7C05EDEE3FCAD12F345A6EE6832D54B758E57394292BA651 com.studio.keypaper2021
CC2DEFEF5A14F9B4B9F27CC9F5BBB0D2FC8A729A2F4EBA20010E81A362D5560C com.pip.editor.camera
007587C4A84D18592BF4EF7AD828D5AAA7D50CADBBF8B0892590DB48CCA7487E org.my.favorites.up.keypaper
08FA33BC138FE4835C15E45D1C1D5A81094E156EEF28D02EA8910D5F8E44D4B8 com.super.color.hairdryer
9E688A36F02DD1B1A9AE4A5C94C1335B14D1B0B1C8901EC8C986B4390E95E760 com.ce1ab3.app.photo.editor
018B705E8577F065AC6F0EDE5A8A1622820B6AEAC77D0284852CEAECF8D8460C com.hit.camera.pip
0E2ACCFA47B782B062CC324704C1F999796F5045D9753423CF7238FE4CABBFA8 com.daynight.keyboard.wallpaper
50D498755486D3739BE5D2292A51C7C3D0ADA6D1A37C89B669A601A324794B06 com.super.star.ringtones

Some of the apps look like this:

McAfee

The researchers said they reported the apps to Google, and the company removed them.

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