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OneGadget

When playing ctf pwn challenges we usually need the one-gadget RCE (remote code execution), which leads to call execve('/bin/sh', NULL, NULL).

This gem provides such gadgets finder, no need to use objdump or IDA-pro every time like a fool 😉

To use this tool, type one_gadget /path/to/libc in command line and enjoy the magic 😆

Installation

Available on RubyGems.org!

$ gem install one_gadget

Note: requires ruby version >= 2.1.0, you can use ruby --version to check.

Supported Architectures

  • i386
  • amd64 (x86-64)
  • aarch64 (ARMv8)

Implementation

OneGadget uses symbolic execution to find the constraints of gadgets to be successful.

The article introducing how I develop this tool can be found on my blog.

Usage

Command Line Interface

SHELL_OUTPUT_OF(one_gadget)
SHELL_OUTPUT_OF(one_gadget /lib/x86_64-linux-gnu/libc.so.6)

x86_64

Given BuildID

SHELL_OUTPUT_OF(one_gadget -b aad7dbe330f23ea00ca63daf793b766b51aceb5d)

build id

Gadgets Near Functions

Why

Consider this scenario when exploiting:

  1. Able to write on GOT (Global Offset Table)
  2. Base address of libc is unknown

In this scenario you can choose to write two low-byte on a GOT entry with one-gadget's two low-byte. If the function offset on GOT is close enough with the one-gadget, you will have at least 1/16 chance of success.

Usage

Reorder gadgets according to the distance of given functions.

SHELL_OUTPUT_OF(one_gadget /lib/x86_64-linux-gnu/libc.so.6 --near exit,mkdir)

near

Regular expression is acceptable.

SHELL_OUTPUT_OF(one_gadget /lib/x86_64-linux-gnu/libc.so.6 --near 'write.*' --raw)

Pass an ELF file as the argument, OneGadget will take all GOT functions for processing.

SHELL_OUTPUT_OF(one_gadget /lib/x86_64-linux-gnu/libc.so.6 --near spec/data/test_near_file.elf --raw)

Show All Gadgets

Sometimes one_gadget finds too many gadgets to show them in one screen, by default gadgets would be filtered automatically according to the difficulty of constraints.

Use option --level 1 to show all gadgets found instead of only those with higher probabilities.

SHELL_OUTPUT_OF(one_gadget /lib/x86_64-linux-gnu/libc.so.6 --level 1)

Other Architectures

i386
SHELL_OUTPUT_OF(one_gadget /lib32/libc.so.6)

i386

AArch64
SHELL_OUTPUT_OF(one_gadget spec/data/aarch64-libc-2.27.so)

aarch64

Combine with Script

Pass your exploit script as one_gadget's arguments, it can try all gadgets one by one, so you don't need to try every possible gadgets manually.

$ one_gadget ./spec/data/libc-2.19.so -s 'echo "offset ->"'

--script

In Ruby Scripts

require 'one_gadget'
RUBY_OUTPUT_OF(OneGadget.gadgets(file: '/lib/x86_64-linux-gnu/libc.so.6'))
# or in shorter way
RUBY_OUTPUT_OF(one_gadget('/lib/x86_64-linux-gnu/libc.so.6', level: 1))
# from build id
RUBY_OUTPUT_OF(one_gadget('b417c0ba7cc5cf06d1d1bed6652cedb9253c60d0'))

To Python Lovers

import subprocess
def one_gadget(filename):
  return [int(i) for i in subprocess.check_output(['one_gadget', '--raw', filename]).decode().split(' ')]

RUBY_OUTPUT_OF(one_gadget('/lib/x86_64-linux-gnu/libc.so.6'))

Make OneGadget Better

Any suggestion or feature request is welcome! Feel free to send a pull request.

Please let me know if you find any libc that make OneGadget fail to find gadgets. And, if you like this work, I'll be happy to be starred 😬