VB2014 paper: Leaving our ZIP undone: how to abuse ZIP to deliver malware apps

Gregory Panakkal explains that there are different ways of looking at APK files – and that sometimes that can have unintended consequences.

Since the close of the VB2014 conference in Seattle in October, we have been sharing VB2014 conference papers as well as video recordings of the presentations. Today, we have added ‘Leaving our ZIP undone: how to abuse ZIP to deliver malware apps’ by Gregory Panakkal (K7 Computing).

“The

Android

system uses two different implementations when processing an APK file,” Gregory Panakkal writes in his VB2014 paper. The

K7 Computing

researcher goes on to explain that during verification, it uses a Java implementation, while a C++ based implementation is used during final extraction.

This may not be bad in itself, except that the two implementations treat APK (

Android Package

) files and their underlying ZIP structure slightly differently, which has led to some pretty serious vulnerabilities.

Most prominent among these was the ‘Master Key’ vulnerability in

Android 4.3

(

Jellybean

) and earlier, which was

discovered

by researchers

Bluebox

in 2013. The vulnerability was caused by the ZIP standard allowing for two of the files contained in the archive to have the very same name. This allowed for a malicious actor to create an APK file with a valid signature, yet with an unvalidated (and thus potentially malicious) component.

In his paper, Gregory looks at the APK format and at various weaknesses and vulnerabilities, some of which may result in anti-virus products failing to scan an APK file properly. He also demonstrated a ‘Chameleon ZIP’ file, a ZIP file that is simultaneously an

Android

APK file, a Java archive and, as an Office document, can be opened by

Open Office

.

You can read the paper

here

in HTML-format, or download it

here

as a PDF (no registration or subscription required). You can download the presentation slides

here

. We have also uploaded the presentation to our

YouTube

channel.

Have you discovered vulnerabilities in even more recent Android versions? Or have you found malicious actors exploiting such vulnerabilities? Why not

submit an abstract

for

VB2015

? The deadline for submissions is 13 March 2015.

Posted on 05 March 2015 by

Martijn Grooten