Transamerica Android App Vulnerability

Summary

Transamerica's servers don't check the integrity of their Android app when it connects to their servers. It is therefore easy to modify the app, adding trojan code that does malicious things. An attacker who can trick people into using the trojaned app can exploit them.

This vulnerability does not affect people who are using the genuine app from the Google Play Store. It would only harm people who are tricked into installing a modified app from a Web site, email, etc.

The Proof of Concept code below merely logs the user id and password, where other apps on the phone can see it, but there's nothing preventing a better programmer from sending that data, and all the other data the app has, out over the Net.

Transamerica should add integrity-checking to their server-side code. Obfuscating their smali code would also be an improvement, with a powerful obfuscator like DashO, not the worthless ProGuard. There is a commercial product named Arxan that claims to prevent this sort of attack; it probably works, but I haven't been able to test it yet.

Proof of Concept: Step by Step

Using the GenyMotion Android emulator, I installed the genuine App from the Google Play Store.

I pulled the APK file from the device with adb, and decoded the APK file with apktool, as shown below.

Adding Trojan Code

I modified the TiBaseActivity.smali file as shown below.

I rebuilt the APK and signed it, as shown below.

Installing the Modified App

I dragged the APK file from the dist/ directory and dropped it on the emulator to install it.

I entered a test username and password into the login form. The user id and password are in the logs, as shown below.

Timeline

I notified Transamerica on April 10, 2015, as shown below.

Update 6-13-15

TransAmerica updated their app on 6-3-15, but it's still vulnerable the same way. Here's the Trojan I used, with the same results.

Updated 6-13-15