Android Code-Signing Weaknesses Put Most Phones at Risk

A weakness in the way Android verifies changes to an app's code allows hackers to turn any application into a malicious Trojan, according to Bluebox.

Android Phone Risk

A flaw in the application security checking on Android operating systems could allow attackers to turn legitimate applications into Trojan horses without ever needing to grab code off the device, researchers at mobile security startup Bluebox Security stated in an analysis published July 5.

Typically, the Android operating system checks that applications are signed by a legitimate developer each time they are launched. Yet researchers at the startup discovered a way to circumvent the check, allowing the modification of applications on the device without setting off alarms in the operating system, Bluebox Chief Technology Officer Jeff Forristal told eWEEK.

"The idea of a normal app being stuck inside the sandbox—and what attackers can do from inside the sandbox—is the risk that the world knows and accepts right now," he said. "This [technique] gives the app the ability to escape the sandbox and do a heck of a lot more."

Bluebox, which will give full details of the issue July 31 to Aug. 1 at the Black Hat conference in Las Vegas, notified Google of the issue in February 2013. Google issued a patch to device manufacturers a month later and is currently scanning for the issue in the Google Play market, a spokesperson for the technology giant told eWEEK.

"We have not seen any evidence of exploitation in Google Play or other app stores via our security scanning tools," the company said in a statement sent to eWEEK. "Google Play scans for this issue—and Verify Apps provides protection for Android users who download apps to their devices outside of Play."

However, manufacturers and carriers are notoriously slow to patch older devices and it's likely that many users will be vulnerable to the issue until they upgrade to a new phone, Grayson Milbourne, security intelligence director at security firm Webroot, told eWEEK. Once their devices are compromised, it will be very difficult to detect the code, he added.

"It is very difficult to remediate and attack like this, where the system cannot detect changes in the application," he said. "In addition, if system-based applications are infected, they cannot be uninstalled, so recovering from the attack will be hard for regular users."

While proof-of-concept code has reportedly been released for the issue, Webroot has not yet found any malware in the wild that has adopted the technique, Milbourne said.

Forristal stressed that the threat posed by the vulnerability depends on the context in which the phone is used. People who only use their phones for calls have little to worry about, while those who also download pirated apps will have to worry a lot more. Some users may even seek out programs that exploit the vulnerabilities as a way to jailbreak their phones to customize the devices, he said.

While Google has fixed the immediate issue, the patch still needs to be widely distributed. Moreover, other, similar security issues may crop up, Forristal said.

"This is not the end of this class of problems," he said. "Further details will be discussed at my Black Hat talk."

Robert Lemos

Robert Lemos

Robert Lemos is an award-winning freelance journalist who has covered information security, cybercrime and technology's impact on society for almost two decades. A former research engineer, he's...