0x9k / one_gadget

A tool for you easy to find the execve gadget in libc.so.6

One Gadget

When playing ctf pwn challenges we usually need the one-gadget of execve('/bin/sh', NULL, NULL).

This gem provides such gadget finder, no need to use IDA-pro every time like a fool.

This work provides the command-line tool one_gadget for easy usage.

Note: Supports amd64 and i386!

Install

Available on RubyGems.org!

gem install one_gadget

Implementation

OneGadget use simple self-implement symbolic execution to find the constraints of gadgets.

The article introducing how I developed this tool can be found here.

Usage

Command Line Tool

one_gadget
# Usage: one_gadget [file] [options]
#     -b, --build-id BuildID           BuildID[sha1] of libc.
#     -f, --[no-]force-file            Force search gadgets in file instead of build id first.
#     -r, --[no-]raw                   Output gadgets offset only, split with one space.
#     -s, --script exploit-script      Run exploit script with all possible gadgets.
#                                      The script will be run as 'exploit-script $offset'.

one_gadget -b 60131540dadc6796cab33388349e6e4e68692053
# 0x4526a execve("/bin/sh", rsp+0x30, environ)
# constraints:
#   [rsp+0x30] == NULL
# 
# 0xef6c4 execve("/bin/sh", rsp+0x50, environ)
# constraints:
#   [rsp+0x50] == NULL
# 
# 0xf0567 execve("/bin/sh", rsp+0x70, environ)
# constraints:
#   [rsp+0x70] == NULL
# 
# 0xcc543 execve("/bin/sh", rcx, r12)
# constraints:
#   rcx == NULL || [rcx] == NULL
#   r12 == NULL || [r12] == NULL
# 
# 0xcc618 execve("/bin/sh", rax, r12)
# constraints:
#   rax == NULL || [rax] == NULL
#   r12 == NULL || [r12] == NULL
# 
# 0xf5b10 execve("/bin/sh", rcx, [rbp-0xf8])
# constraints:
#   [rbp-0xf8] == NULL || [[rbp-0xf8]] == NULL
#   rcx == NULL || [rcx] == NULL

one_gadget /lib/i386-linux-gnu/libc.so.6
# 0x3ac69 execve("/bin/sh", esp+0x34, environ)
# constraints:
#   esi is the address of `rw-p` area of libc
#   [esp+0x34] == NULL
# 
# 0x5fbc5 execl("/bin/sh", eax)
# constraints:
#   esi is the address of `rw-p` area of libc
#   eax == NULL
# 
# 0x5fbc6 execl("/bin/sh", [esp])
# constraints:
#   esi is the address of `rw-p` area of libc
#   [esp] == NULL

Combine with exploit 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 ->"'

Directly use in script

require 'one_gadget'
OneGadget.gadgets(file: '/lib/x86_64-linux-gnu/libc.so.6')
# => [283242, 980676, 984423, 836931, 837144, 1006352]
# or in shorter way
one_gadget(file: '/lib/x86_64-linux-gnu/libc.so.6')
# => [283242, 980676, 984423, 836931, 837144, 1006352]

# from build id
one_gadget(build_id: '60131540dadc6796cab33388349e6e4e68692053')
# => [283242, 980676, 984423, 836931, 837144, 1006352]

Screenshots

Search gadgets from file

64 bit

32 bit

Fetch gadgets from database