Using reverse engineering techniques to see how a common malware packer works
UPX (Ultimate Packer for eXecutables) is an open source executable packer that is common in the malware scene (albeit often heavily modified). UPX supports all major operating systems and both x86 and x64 platforms. UPX on its own features no anti-debug checks, no scrambled code/stolen bytes and no encryption. For this post I have coded my own software in the C language to demonstrate how UPX works, what it does to the .code/.data segment in the PE header and how you can rebuild an executable that has been packed with UPX.cram