DoubleLocker, the Android Ransomware that encrypts files and changes PIN Lock

Pierluigi Paganini October 14, 2017

Crooks have developed a strain of Android ransomware dubbed Doublelocker that both encrypts user data and changes PIN Lock.

DoubleLocker, the name says it all, is a new malware that not only encrypts the Android mobile devices but also changes PIN lock.

The DoubleLocker ransomware was discovered by security researchers from cybersecurity firm ESET.

DoubleLocker is the first-ever ransomware to abuse the Android accessibility feature that implements alternative ways to interact with a mobile device.

The Android accessibility services are abused by several mobile malware including banking Trojan and adware.

“Given its banking malware roots, DoubleLocker may well be turned into what could be called ransom-bankers.” explained Lukáš Štefanko, the ESET malware researcher who discovered DoubleLocker. “Two-stage malware that first tries to wipe your bank or PayPal account and subsequently locks your device and data to request a ransom… Speculation aside, we spotted a test version of such a ransom-banker in the wild as long ago as May, 2017.”

Researchers first detected the DoubleLocker ransomware in May, crooks spread it as a fake Adobe Flash update via compromised websites.

Once the victim launched the app, it requests activation of the malware’s accessibility service, named “Google Play Service”. Once the malicious code has obtained the accessibility permissions, it uses them to activate device administrator rights and set itself as the default Home application without the user’s consent.

“Setting itself as a default home app – a launcher – is a trick that improves the malware’s persistence. Whenever the user clicks on the home button, the ransomware gets activated and the device gets locked again. Thanks to using the accessibility service, the user doesn’t know that they launch malware by hitting Home,” explains Štefanko.

DoubleLockerr, once executed on the device, first changes the device PIN to a random value that neither crooks know nor stored anywhere. At the same time, the ransomware encrypts all the files using AES encryption algorithm, it appends the extension “.cryeye” to each file.

Unfortunately, encryption process has no bugs making impossible to recover the files without receiving the encryption key from the crooks.

The ransomware demands 0.0130 BTC (approximately USD 73.83 at time of writing). the ransom payment must be completed within 24 hours.

doublelocker android ransomware

If the victim pays the ransom, he will receive the decryption key to unlock the files and the crooks will remotely reset the PIN to unlock the victim’s device.

The researchers highlighted that there is no way to unlock encrypted files for non-rooted devices, in this case, the unique way to clean the device is to factory-reset their phone.

Users with rooted Android devices with debugging mode enabled can use the Android Debug Bridge (ADB) tool to reset PIN without formatting their phones.

“For rooted devices, however, there is a method to get past the PIN lock without a factory reset. For the method to work, the device needed to be in the debugging mode before the ransomware got activated.” reads the analysis from ESET.

As usual, the best way to protect your device is to install applications only from trusted stores, like Google Play and pay attention to the reputation of the developers.

Be vigilant with any links provided in an unsolicited email, SMS or instant messaging app message.

Do not forget to install an antivirus app on your mobile device and keep all running software up-to-date.

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Pierluigi Paganini

(Security Affairs – Doublelocker ransomware, mobile)

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