(UPDATE See post #3)

Earlier last month, RFP from BlueBox published a sneak preview of his upcoming BlackHat talk, detailing a vulnerability in the Android platform that affects nearly all Android devices. Soon after, a vulnerability of similar nature and impact was published on Chinese forum. Both of these "Master Key" vulnerabilities allow an attacker to modify the code of an Android package without affecting the signature of the package as verified by the package manager, which has serious implications when considering system-signed packages. From an end user perspective, the vulnerabilities allow an attacker to take full control of a user's device.

Google will be issuing a fix for this in their newer releases of Android firmware. However, these fixes will take time to filter down the food chain from Google to carriers to users... if indeed, a firmware update is even issued for older devices that are now past End of Life, since this vulnerability affects 99% of all Android devices going back to Android 1.6, Donut.

Not wishing to take a chance, I have installed an app, free from the Play Store, which is the result of a research collaboration between Duo Security, a cloud-based two-factor authentication and mobile security company, and Northeastern University's System Security Lab (NEU SecLab) and patches the, "Master Key", vulnerabilities on rooted devices.

The patch is not phone, device or firmware specific... you can whack it on any Android device that is rooted. Once activated it patches the device but should you flash a different firmware you will need to patch it again.

The app is ReKey and can be downloaded from the Play Store

Download

Source

 

UPDATE

In reality, because the S4's firmware is so new, that certainly the later updates should have the Google patch to fix the bug, 8219321. However, other Android devices that are older and have not received a recent build firmware update, will be at risk.

Since writing post #1, I have uninstalled ReKey and run a test using the newly released, SRT AppScanner, free from the Play Store. This confirmed that on my current firmware, MGA, build date 11 JUL; that there is no vulnerability to the Bluebox bug 8219321 and that ReKey is not required.

However, perhaps just as worryingly, the second, more recent, Master Key bug 9695860, usually referred to as the, "Chinese Master Key bug", has not been patched by Google in this firmware and is not covered by ReKey. This bug, only discovered very recently, is already patched by Google in the very latest versions of code for Android, (commit), but as yet, has not made its way down the chain for release.

There has in the last few days, been a Universal fix released for both the 8219321 and 9695860 bugs but this entails flashing a framework to your phone before applying the Universal Fix.

For more details on this, see Tungstwenty's xda thread, here.

The bottom line is that if you currently want protection from both of these bugs then Dual Fix is the way to go until a firmware for your device is released that patches both vulnerabilities. Which, in the case of older devices, might be never.

Below are 2 screenshots from SRT AppScanner showing that whilst ReKey has indeed patched one bug, the device is still vulnerable to the latest one. The 2nd screenhot shows the device after installing the framework .apk and Dual Fix .apk...

ReKey Fix only




Dual Fix

 

I am given to understand that CM10.1.2 has both fixes already installed.

Have updated my previous post with some screenshots as I have now implemented the Dual Bug Fix.

 

The first hacks using the Master Key have already been detected...

Hackers use Android 'master key' exploit in China

 

It would appear that cyber criminals are not slow to catch on to the Android Master Key exploits and more examples are cropping up...

More Exploits for Android 'MasterKey' Vulnerability Turn Up in the Wild

Researchers find trojanized banking app that exploits critical Android bug

The chances are that if you have received a firmware update for your device in the last 3 or 4 months, it will have a fix for 1 of the 2 identified exploits, Bug #8219321, but not the Bug #9695860 which Android has also issued a patch for but, as yet, has not made its way to any firmware releases yet.

You can check to see which of the Bugs you are vulnerable to by installing and running SRT AppScanner, free from the Google Play Store.

App developers are also starting to take these exploits seriously...

Android Flaw Puts Bitcoin Wallet Apps at Risk of Theft

Some degree of protection is offered by only using the Google Play Store and ensuring that installing apps from, "Unknown sources", is deselected on your device. Antivirus software will not prevent the Master Key exploits and may, or may not, detect them after installation.

You should also ensure that you have the very latest firmware installed for your device.

In the meantime, for rooted users, there is the fix mentioned earlier.

 

Sighs! Sadly Syd... I have come to accept the fact that some people are just not good with instructions and explanations, as this video demonstrates...

Instructions and Explanations

 

I must admit that I did it the other way round and flashed Xposed first and then Dual Fix and then have updated 3Minit a few times thereafter. I can't see that it would cause a problem. Do a nandroid first and if there are any issues, do Xposed and then 3Minit.

 

In the immortal words of Del Boy of Only Fools and Horses fame...

"He who dares Rodney... He who dares"

 

On the grounds that we haven't heard from sntaylor since... and Syd did say that it worked for him, doing it the opposite way to you and I, Rudedawg... it is a little worrying! :vamp: