Computer scientists have discovered a weakness in smartphones running Google's Android operating system that allows attackers to secretly record phone conversations, monitor geographic location data, and access other sensitive resources without permission.

Handsets sold by HTC, Samsung, Motorola, and Google contain code that exposes powerful capabilities to untrusted apps, scientists from North Carolina State University said. These “explicit capability leaks” bypass key security defenses built into Android that require users to clearly grant permission before an app gets access to personal information and functions such as text messaging. The code making the circumvention possible is contained in interfaces and services the device manufactures add to enhance the stock firmware supplied by Google.

“We believe these results demonstrate that capability leaks constitute a tangible security weakness for many Android smartphones in the market today,” the researchers wrote in a paper (PDF) scheduled to be presented at next year's Network and Distributed System Security Symposium. “Particularly, smartphones with more pre-loaded apps tend to be more likely to have explicit capability leaks.”

The researchers created a diagnostic app dubbed Woodpecker and ran it on eight smartphones from the four vendors. The most vulnerable was HTC's EVO 4G device, which was found to leak eight functions, including its precise geographic location finder, camera, text message service, and audio recorder. HTC's Legend came in second with six leaks. Samsung's Epic 4G contained three leaks, including the ability to wipe data and applications off the handset. Google's Nexus One and Nexus S contained one leak.

Unlike out-of-the-box iPhones, which allow users to install only apps that have been approved by Apple, the official Android Market performs no security checks on the wares it offers. To compensate, Google built the permission-based security model into the mobile OS to give users control over the personal information apps get to access. Before a new program runs for the first time, it lists the sensitive resources it will access. Users who are uncomfortable with the permissions then have an opportunity to cancel the installation.

The researchers found that the manufacturer-supplied enhancements offer a way to circumvent this permissions-based model. In a video demonstration, they show how an app they designed is able to access audio-recording and SMS functions on an EVO 4G without first getting approval from the user. As a result, the app is able to turn on a recorder that collects nearby audio or phone conversations. The app is also able to send unauthorized text messages.

The researchers said both Google and Motorola have confirmed the vulnerabilities in their handsets, but that HTC and Samsung “have been really slow in responding to, if not ignoring, our reports/inquiries.”

The North Carolina State University scientists are the same team that has uncovered other serious security vulnerabilities in Android-powered smartphones, including the infiltration of at least 12 malicious apps in the Android Market. The data-stealing programs festered there for months and racked up hundreds of thousands of downloads. They were removed only after the researchers alerted Google to their presence.

The researchers say other Android handset models may also be vulnerable to the latest permissions-bypass attack. ®

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