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Blackphone Gets Another Security Black Eye

The super-secure Blackphone is designed to let its users text and call with top-notch security and privacy. But a recently discovered flaw in Blackphone's encrypted messaging app, Silent Text, left Blackphone users vulnerable. Just by knowing a Blackphone user's phone number or ID, an attacker could have exploited the flaw to decrypt messages, steal contact lists or even seize control of parts of the device itself.

The good news is, the bug was discovered by security researcher Mark Dowd of Sydney-based Azimuth Security, who privately reported it to Blackphone's manufacturers. Both Silent Text and Blackphone itself have already received patches for the flaw in their respective latest updates.

MORE: 7 Ways to NSA-Proof Your Smartphone

With these updates, Blackphone users should be protected from exploits of this flaw. But the fact that a flaw of this size and seriousness even existed is a reminder that nothing, not even a device designed to prioritize security and privacy above all, is ever 100 percent secure.

According to Dowd's very in-depth blog post, the vulnerability itself was a type-confusion flaw, a kind of memory corruption whereby the software confuses an object's data type.  These types of errors are fairly common in all kinds of software. 

To exploit this particular instance of type confusion flaw on Blackphone, attackers could use a target's phone number or Blackphone ID to remotely send the target a specially crafted message. The Silent Text app would then mistakenly interpret that message as a miniature program instead of a block of text. The program then rewrites a pointer in the device's memory.

After that, attackers could access the Blackphone's decrypted messages and contact list, as well as look at the phone's GPS location, write code to the phone's external storage, and see how many accounts are stored on the Blackphone.

The flaw was quite serious, but Blackphone seems to have handled it very well: The company worked with Dowd to quickly patch the issue, and Dowd only disclosed the flaw after the update had gone out to users.

This isn't the first time Blackphone has been dinged for a security flaw. Last August, security researcher Jon "Justin Case" Sawyer found three flaws immediately after buying a Blackphone at the DEF CON hacker conference in Las Vegas. One flaw existed only in the first model run of the handset, and another had already been patched, but Sawyer said he was keeping the third under wraps to conduct further research.

Jill Scharr is a staff writer for Tom's Guide, where she regularly covers security, 3D printing and video games. You can follow Jill on Twitter @JillScharr and on Google+Follow us @tomsguide, on Facebook and on Google+.