Security Experts:

Android Vulnerability Lets Attackers Convert Legitimate Apps into Trojans

Researchers recently uncovered a serious vulnerability in Android which would allow attackers to modify apps without affecting the cryptographic signature.

With this flaw, attackers could easily turn legitimate apps into Trojans, Jeff Forristal, CTO of Bluebox Security, wrote in the company blog on Wednesday. The vulnerability has been present since at last Android 1.6, also known as Donut, according to Bluebox Labs researchers. This means any Android phone released in the last four years, which accounts for approximately 900 million users, could be vulnerable, Forristal said.

Google has fixed the security hole in Android, but it would be up to handset manufacturers to produce and release firmware updates for mobile devices to close the flaws. Users also need to install those updates as soon as they are available.

Android Vulnerability"The implications are huge!" Forristal wrote in the blog.

All Android apps have cryptographic signatures, which lets users determine if the app is legitimate and that it hasn't been tampered with. There is a discrepancy in how apps are cryptographically verified and installed, which allows the attacker to modify the app's APK without breaking its cryptographic signature, Forristal said.

Essentially, the malicious author tricks Android into believing the app is unchanged even if it has been, Forristal said. Any app can be turned into a malicious Trojan which would be completely unnoticed by the app store, the phone, or the end user," he wrote.

There are two possible bad-news scenarios.

One, is that an individual may download an app from Google Play thinking it was legitimate, and find out it was actually a data-stealing Trojan. That Trojanized app can harvest data from the device and gain access to sensitive corporate data and systems.

The second scenario, however, doesn't even need the user to download an app. Many handset makers make their own apps that are granted special elevated privileges on the device, Forristal said. These apps have system-level access, and has access to the full operating system and all applications currently installed. If one of these gets swapped out with a malicious version, then the attacker has full read access on the device, can retrieve all saved information such as passwords, and take over the phone's functionality.

Bluebox Labs researchers were able to modify an Android device manufacturer’s application to gain all permissions on the device, Forristal said. Further details will be disclosed during the Black Hat conference in Las Vegas at the end of the month.

Device owners should be extra cautious in identifying the publisher of the app they want to download, Bluebox Security recommended. This isn't an issue just with apps from the handset makers—third-parties partner with device manufacturers—such as Cisco with AnyConnect VPN.

Mobile security can't just be about device management. IT needs to focus deep device integrity checking and securing corporate data, Forristal wrote in the post.

Enterprises "should use this news to prompt all users to update their devices, and to highlight the importance of keeping their devices updated," Forristal said.

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Fahmida Y. Rashid is a Senior Contributing Writer for SecurityWeek. She has experience writing and reviewing security, core Internet infrastructure, open source, networking, and storage. Before setting out her journalism shingle, she spent nine years as a help-desk technician, software and Web application developer, network administrator, and technology consultant.