February 24, 2016

Decipher Updates of a Popular 4G Modem: Dmitry Sklyarov’s Method

What could a reverse engineer do if trying to examine device code he couldn’t find anything except encrypted firmware files? Here is a real story how to meet the challenge with basic knowledge of computer science and mere logic.

We do not specify the modem vendor or exact names of the files deliberately — this article focuses on the challenge and an interesting approach to the solution. This method is not applicable to the latest models of the modem, but it might work with older ones and other vendors.

February 4, 2016

PayPal Remote Code Execution

In December 2015, I found a critical vulnerability in one of PayPal business websites ( It allowed me to execute arbitrary shell commands on PayPal web servers via unsafe Java object deserialization and to access production databases. I immediately reported this bug to PayPal security team, and it was fixed promptly.