Cross Arch Shellcode Compiler

2016 - ixty

Information

This program allows to build portable, architecture independant shellcode from C code. It currently supports the following architectures:

• x86
• x86_64
• arm
• arm_64

It works by:

• compiling the same C code for each architecture
• linking it to arch specific syscall implementation
• using a polyglot dispatching shellcode

The final layout of the output binary is: [ DISPATCHER ] [ X86 BLOCK ] [ X86_64 BLOCK ] [ ARM BLOCK ] [ ARM_64 BLOCK ]

The dispatcher is in stage0 Open stage0/README for information on how it works

Each arch specific block has the following layout:

[ LOADER    ]
[ RELOC NUM ]
[ RELOC 0   ]
[ RELOC 1   ]
    ...
[ RELOC N   ]
[ START OFF ]
[ CODE      ]

Open stage1/README for information on loaders

The final payload code is the stage2. Open stage2/README for information on the payload

Dependencies

• python2.7
• nasm
• gcc
• pyelftools (pip install pyelftools)
• qemu-user-static
• qemu-utils
• arm chroot with gcc
• arm64 chroot with gcc

Assuming you use debian:

# apt-get install gcc nasm python2.7 python-pip
# apt-get install qemu qemu-user-static qemu-utils binfmt-support debootstrap
# qemu-debootstrap --arch=arm64 jessie /opt/arm64/ http://ftp.debian.org/debian
# qemu-debootstrap --arch=armhf jessie /opt/armhfxx/ http://ftp.debian.org/debian

# chroot /opt/arm64
# apt-get install gcc
# exit

# chroot /opt/armhf
# apt-get install gcc
# exit

Running & testing

$ ./build.py

If everything goes well, it creates ./ouput which is the portable multi-arch shellcode.

To test that everything works, use the provided 'sc' utility:

On the local x86_64 machine
user@x86_64-box   $ ./sc_86     ./output
user@x86_64-box   $ ./sc_x86_64 ./output
... And in the chroots for arm/arm64
user@armhf-chroot $ ./sc_arm    ./output
user@arm64-chroot $ ./sc_arm_64 ./output

Credits

Thanks to feliam

https://github.com/feliam/mkShellcode

http://blog.binamuse.com/2013/01/about-shellcodes-in-c.html

The x86 / x86_64 loader code is taken from this project and the shellcode extraction technique is based upon his work aswell.