Android ransomware downloads malicious apps that lock your device

A new breed of Android malware that automatically downloads malicious apps was uncovered by security researchers after it attacked one of their company's test devices.

The exploit kit, which is the first stage of the attack, is delivered via a malicious ad on a website (also known as malvertising) that contains hostile Javascript, according to security firm Blue Coat.

The kit then installs ransomware masquerading as an app onto the Android device.

This ransomware executes automatically at a time of the malware author's choosing. When executed, it poses as a message from fake law enforcement agency Cyber.Police, with the seals of the FBI and NSA also displayed to give it an additional level of credibility.

This veneer of credibility is almost immediately undermined, however, as it demands payment in iTunes gift cards.

The malware itself is in fact quite crude - rather than encrypting the whole device and all the files contained on it, as most modern ransomware does, it instead simply locks it.

While quite old fashioned in this respect, Blue Coat researcher Andrew Brandt said this was the first time "an exploit kit has been able to successfully install malicious apps on a mobile device without any user interaction on the part of the victim".

"During the attack, the device did not display the normal 'application permissions' dialog box that typically precedes installation of an Android application," he said in a blog post.

In consultation with another researcher, Joshua Drake of Zimperium, it was determined that the malicious Javascript used at the beginning of the attack "contains an exploit against libxslt that was leaked during the Hacking Team breach".

"The commoditised implementation of the Hacking Team ... exploits to install malware onto Android mobile devices using an automated exploit kit has some serious consequences," said Brandt.

"The most important of these is that older devices, which have not been updated (nor are likely to be updated) with the latest version of Android, may remain susceptible to this type of attack in perpetuity. That includes so-called media player devices - basically inexpensive, Android-driven video playback devices meant to be connected to TVs - many of which run the 4.x branch of the Android OS," he added.

While there is little a user can do to protect against the attack if they are unable to upgrade from a vulnerable operating system, they can take mitigating steps by regularly backing up their device.

That way, if they are attacked by this malware or others, they can reset the device to factory default and restore from backup without losing very much or any data.