py-shelf 3

Python package to create shellcodes from elfs supported arch (mips, arm (32bit), i386 32bit, i386 64bit, aarch64)

Shelf - Shellcode ELF convert elf to shellcode

Convert standard elf files to standalone shellcodes. Please read the following documentation and view the examples for this project to work properly

Project links

Github

Pypi

Supported architectures

• mips
• i386 (32bit)
• i386 (64bit)
• arm (32bit)
• aarch64 (arm 64 bit)

Installation:

pip install py_shelf

Python version support

• python3

How does this work ?

The python library parses the elf and create a simple relocatable file format Then the mini loader is inserted as the entry point of the elf the mini loader will load the relocatable format and execute it. There are no special requirements, the library contain the compiled mini loaders.

  classDiagram
    ShellcodeEntryPoint --|> MiniLoader
    ShellcodeEntryPoint: Shellcode to jump into the mini loader
    MiniLoader --|> Relocation table
    MiniLoader: Contain all the logic for parsing the relocation table
    MiniLoader: fully os independent
    Relocation table --|> SHELF
    Relocation table : Contain table required for shellcode runtime relocation
    SHELF: Shellcode elf - This is the compiled binary we convert into shellcode
    SHELF: This binary is stripped into only opcodes
    SHELF: fully relocatable using the relocation table

This project is intended to convert elf to os independent shellcodes. Therefor the loader never allocate memory and the shellcode format is not packed. You can just execute it, eg ...

((void (*)()) shellcode)();

note that __libc_start_main perform syscalls therefor if you want your shellcode to be fully os independent you must compile with -nostartfiles follow the examples below

Creating a shellcode

Some compilation flags are required for this to work properly. You must compile the binary with -fPIE and -static take a look at the provided examples below (makefile).

shellcode is a stripped binary with no symbols and no elf information only opcodes, in order to make the shellcode this library require a binary with elf information. so make sure you are not stripping the binary before using this library

simplified make command for mips big endian

gcc example.c -fno-stack-protector -fPIE -fpic -static -nostartfiles --entry=main -o binary.out
python -m shelf --input binary.out                                     

Examples:

Makefile

Example.c

Testing your shellcode

You can use the provided shellcode Loader to test you shellcodes

qemu-mips ./shellcode_loader ./myshellcode.out

Output example

Shellcode size = 66620
Allocating shellcode buffer, size = 69632
Mapping new memory, size = 69632
Jumping to shellcode, address = 0x7f7ee000
Hello from shellcode !

Advanced concepts and features

for following links only work on the github page

• Compiling with libc
• Dynamic shellcode
• Hooking the mini loader
• Mitigation bypass
• Optimizations
• Output formats
• Development
• Specific architecture limitations