I have been working at viaForensics as the Director of R&D for about 5 months now, and in that time I’ve been involved in some exciting research projects. I haven’t had the opportunity to blog on our company site yet so I thought I’d take a little time out and record a video to demonstrate an Android issue that is of interest to many of our clients.
When talking with people and reading posts on the web I’ve often heard people say that the Android permission system protects their device such that apps without certain permissions are therefore safe to install. The permissions system on Android is a fantastic idea and generally well implemented, it gives apps just enough permissions or capabilities to perform the required functions without exposing capabilities that could be used in a dangerous way. It is a step up in protection when compared with a typical desktop system but this increased protection can give rise to a false sense of security.
Putting aside the issue of users ignoring the permissions when installing apps, can we rely solely on permissions to decide if an app is safe? There are multiple controls in Android and its ecosystem that protect a user and their device, but one should not automatically assume that installing an app, even if it requires no permissions, is safe.
To demonstrate this we’ve built an app which requires no permissions and yet is able to give an attacker a remote shell and allow them to execute commands on the device remotely from anywhere in the world. The functionality we are exploiting to do this is not new, it has been quietly pointed out for a number of years, and was explained in depth at Defcon 18 . It is not a zero-day exploit or a root exploit. We are using Android the way it was designed to work, but in a clever way in order to establish a 2-way communication channel. This has been tested on Android versions ranging from 1.5 up to 4.0 Ice Cream Sandwich, and it works in a similar way on all platforms.
Please see the video below with accompanying audio for further explanation.
Link to video: Android No-permissions Reverse Shell
I should also mention here a recent paper by Michael Grace, Yajin Zhou, Zhi Wang, and Xuxian Jiang from NCSU who have developed a tool to detect capability leaks in Android devices. Using their tool they found a number of capability leaks, such as being able to send an SMS, in various Android applications usually added by OEMs. Malicious applications can call the vulnerable apps and exploit the lack of protection around permission/capability use and therefore do not need to request permissions themselves. In a similar way we’ve exploited the Android Web Browser, although we are not exploiting a vulnerability due to bad coding, but rather using the functionality it legitimately offers to other applications.
In this demonstration Android’s power and flexibility were perhaps also its downfall. Other smartphone platforms may not offer the controls we are bypassing at all, and the multi-tasking capabilities in Android allowed us to run the attack almost transparently to the user. This power combined with the open nature of Android also facilitates the customisation of the system to meet bespoke security requirements. This is something we have even been involved in ourselves by implementing a proof of concept Loadable Kernel Module to pro-actively monitor and defend a client’s intellectual property as it passed through their devices. It is no surprise that we have seen adoption of Android research projects in the military and government as it can be enhanced and adapted for specific security requirements, perhaps like no other mobile platform before it.
I hope this demo was of interest and that it generates some discussion around the best ways to select and use apps which offer the least risk to your device and data.
Update 20-Dec-2011: As mentioned these issues are not new and have been discussed before. Updated to include a link to one such talk which does a good job of explaining some of the issues (thanks Tim):
 Defcon 18 Presentation “These Aren’t The Permissions You’re Looking For” by Tim Wyatt, David Luke Richardson and Anthony Lineberry. PDF Link.