UNCOVERING ANDROID MASTER KEY THAT MAKES 99% OF DEVICES VULNERABLE

RECENTLY discovered a vulnerability in Android’s security model that allows a hacker to modify APK code without breaking an application’s cryptographic signature, to turn any legitimate application into a malicious Trojan, completely unnoticed by the app store, the phone, or the end user. The implications are huge! This vulnerability, around at least since the release of Android 1.6 (codename: “Donut” ), could affect any Android phone released in the last 4 years1 – or nearly 900 million devices2– and depending on the type of application, a hacker can exploit the vulnerability for anything from data theft to creation of a mobile botnet.

While the risk to the individual and the enterprise is great (a malicious app can access individual data, or gain entry into an enterprise), this risk is compounded when you consider applications developed by the device manufacturers (e.g. HTC, Samsung, Motorola, LG) or third-parties that work in cooperation with the device manufacturer (e.g. Cisco with AnyConnect VPN) – that are granted special elevated privileges within Android – specifically System UID access.

Installation of a Trojan application from the device manufacturer can grant the application full access to Android system and all applications (and their data) currently installed. The application then not only has the ability to read arbitrary application data on the device (email, SMS messages, documents, etc.), retrieve all stored account & service passwords, it can essentially take over the normal functioning of the phone and control any function thereof (make arbitrary phone calls, send arbitrary SMS messages, turn on the camera, and record calls). Finally, and most unsettling, is the potential for a hacker to take advantage of the always-on, always-connected, and always-moving (therefore hard-to-detect) nature of these “zombie” mobile devices to create a botnet.

How it works:

The vulnerability involves discrepancies in how Android applications are cryptographically verified & installed, allowing for APK code modification without breaking the cryptographic signature.

All Android applications contain cryptographic signatures, which Android uses to determine if the app is legitimate and to verify that the app hasn’t been tampered with or modified. This vulnerability makes it possible to change an application’s code without affecting the cryptographic signature of the application – essentially allowing a malicious author to trick Android into believing the app is unchanged even if it has been.

Details of Android security bug 8219321 were responsibly disclosed through Bluebox Security’s close relationship with Google in February 2013. It’s up to device manufacturers to produce and release firmware updates for mobile devices (and furthermore for users to install these updates). The availability of these updates will widely vary depending upon the manufacturer and model in question.

The screenshot below demonstrates that Bluebox Security has been able to modify an Android device manufacturer’s application to the level that we now have access to any (and all) permissions on the device. In this case, we have modified the system-level software information about this device to include the name “Bluebox” in the Baseband Version string (a value normally controlled & configured by the system firmware).

Screenshot of HTC Phone After Exploit




Recommendations
Device owners should be extra cautious in identifying the publisher of the app they want to download.
Enterprises with BYOD implementations should use this news to prompt all users to update their devices, and to highlight the importance of keeping their devices updated.
IT should see this vulnerability as another driver to move beyond just device management to focus on deep device integrity checking and securing corporate data.

1. http://developer.android.com/about/dashboards/index.html

2. http://venturebeat.com/2013/05/15/900m-android-activations-to-date-google-says/

Bluebox offered the following;


“The vulnerability involves discrepancies in how Android applications are cryptographically verified & installed, allowing for APK code modification without breaking the cryptographic signature.”

They also went on to mention about how all Android apps contain a cryptographic signature and that is what Android uses to see if the app is legitimate. Or more to the point, to see if that app has been tampered with in any way. Basically, by being able to do this without breaking the signature — it would have been easy (for someone with the right knowledge) to trick Android into thinking a malicious app was perfectly harmless.

Otherwise, while Google has taken care of the Play Store, the rest of the update/fix process is up to the carriers and manufacturers. Bluebox Security has also said they will be discussing more of the technical details of this issue during Black Hat USA 2013 which runs from July 27th through August 1st.