Privacy is a hot topic at the moment - it continues to dominate the headlines as news of new NSA incursions, celebrity phone hacks, and corporate breaches are being reported on an increasingly regular basis. In response to this, a number of products have been brought to market that attempt to provide consumers with a greater level of privacy than typical devices allow for. In the phone market, one of the premier products to be released in recent years is undoubtedly the BlackPhone (http://www.blackphone.ch), which has been cited numerous times in tech publications as being one of the best available defenses against mass surveillance, as it provides full end-to-end encryption facilities for voice calls and text/MMS messaging.

While exploring my recently purchased BlackPhone, I discovered that the messaging application contains a serious memory corruption vulnerability that can be triggered remotely by an attacker.  If exploited successfully, this flaw could be used to gain remote arbitrary code execution on the target's handset. The code run by the attacker will have the privileges of the messaging application, which is a standard Android application with some additional privileges. Specifically, it is possible to:

• decrypt messages / commandeer SilentCircle account
• gather location information
• read contacts
• write to external storage
• run additional code of the attacker's choosing (such as a privilege escalation exploit aimed at gaining root or kernel-mode access, thus taking complete control of the phone)

The only knowledge required by the attacker is the target's Silent Circle ID or phone number - the target does not need to be lured in to contacting the attacker (although the flaw is exploitable in this scenario as well).

This issue is now patched by both Silent Circle and Blackphone in the respective App Stores / Product updates.

The remainder of this post discusses the technical details of this vulnerability, citing the source code of the vulnerable application where appropriate. This code is available from Silent Circle's github repository (https://github.com/SilentCircle).