This presentation is a case study showcasing the technical details of Android security bug 8219321, disclosed to Google in February 2013. The vulnerability involves discrepancies in how Android applications are cryptographically verified & installed, allowing for APK code modification without breaking the cryptographic signature; that in turn is a simple step away from system access & control. The vulnerability affects a wide number of Android devices, across generations & architectures, with little to no modifications of the exploit. The presentation will review how the vulnerability was located, how an exploit was created, and why the exploit works, giving you insight into the vulnerability problem and the exploitation process. Working PoCs for major Android device vendors will be made available to coincide with the presentation.