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First Malicious Apps Targeting Android ‘Master Key Vulnerability’ Found in the Wild

Earlier this month, researchers from Bluebox Security uncovered a serious vulnerability in Android that allowed for the modification of apps without affecting the cryptographic signature, making it possible for attackers to turn legitimate apps into Trojans.

Earlier this month, researchers from Bluebox Security uncovered a serious vulnerability in Android that allowed for the modification of apps without affecting the cryptographic signature, making it possible for attackers to turn legitimate apps into Trojans.

Shortly after the “master key vulnerability” was uncovered, Proof-of-concept code for exploiting it was found on the Internet.

Now, Symantec says it has uncovered the first malicious apps making use of the exploit in the wild.

iOS Apps as Invasive as Android Apps

“We expected the vulnerability to be leveraged quickly due to ease of exploitation, and it has,” Symantec said. 

Symantec discovered two mobile applications that were infected by an attacker, which are legitimate applications used to help find and make doctor appointments and distributed on Android marketplaces in China.

“An attacker has taken both of these applications and added code to allow them to remotely control devices, steal sensitive data such as IMEI and phone numbers, send premium SMS messages, and disable a few Chinese mobile security software applications by using root commands, if available,” Symantec explained in a blog post.

By exploiting the master key vulnerability, the attacker was able to modify the original Android application by adding an additional classes.dex file, which contains the Android application code. The attackers also added an additional Android manifest file, which specifies permissions, Symantec said.

Android Master Key Vulnerability Exploited

Snippet of Injection Code Targeting Android Master Key Vulnerability. (Image Credit: Symantec)

While this may be the first instance discovered where attackers have exploited the vulnerability, researchers expect attackers to continue to leverage the vulnerability to infect Android devices, especially as more technical details of the vulnerability emerge.

Jeff Forristal, CTO of Bluebox Security, plans to share the technical details of the vulnerability in his upcoming Black Hat USA 2013 talk, where he plans to review the bug, including how it was found, and the details behind how it works. 

The flaw, discussed here in a SecurityWeek podcast with Bluebox co-founder Adam Ely, has been present since at least Android 1.6 – making it roughly four years old.

Google has fixed the security hole in Android, but it is now in the control of handset manufacturers to produce and release the updates for mobile devices to patch the flaws. Some of Google’s OEM partners, such as Samsung, are already shipping a fix to their Android devices, Google told SecurityWeek

Bluebox Security has released a free app designed to help Android users check if their device has been patched for the master key vulnerability.

As always, users should only download applications from reputable Android application marketplaces.

Symantec detects the malicious applications as Android.Skullkey.  

Related Podcast: Bluebox’s Adam Ely Discusses Android Master Key Vulnerability

Related Reading: Android Vulnerability Lets Attackers Convert Legitimate Apps into Trojans

Related Reading: iOS Apps Just as Intrusive as Android Apps

Written By

For more than 10 years, Mike Lennon has been closely monitoring the threat landscape and analyzing trends in the National Security and enterprise cybersecurity space. In his role at SecurityWeek, he oversees the editorial direction of the publication and is the Director of several leading security industry conferences around the world.

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