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https://github.com/david942j/one_gadget

The best tool for finding one gadget RCE in libc.so.6
https://github.com/david942j/one_gadget

ctf exploit gadget glibc libc one-gadget-rce pwn pwnable shell

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The best tool for finding one gadget RCE in libc.so.6

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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 :wink:



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



## Installation



Available on RubyGems.org!

```bash

$ gem install one_gadget

```



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



## Supported Architectures



- [x] i386

- [x] amd64 (x86-64)

- [x] 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](https://david942j.blogspot.com/2017/02/project-one-gadget-in-glibc.html).



## Usage



### Command Line Interface



```bash

$ one_gadget

# Usage: one_gadget  [options]

#     -b, --build-id BuildID           BuildID[sha1] of libc.

#     -f, --[no-]force-file            Force search gadgets in file instead of build id first.

#     -l, --level OUTPUT_LEVEL         The output level.

#                                      OneGadget automatically selects gadgets with higher successful probability.

#                                      Increase this level to ask OneGadget show more gadgets it found.

#                                      Default: 0

#     -n, --near FUNCTIONS/FILE        Order gadgets by their distance to the given functions or to the GOT functions of the given file.

#     -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'.

#         --info BuildID               Show version information given BuildID.

#         --base BASE_ADDRESS          The base address of libc.

#                                      Default: 0

#         --version                    Current gem version.



```



```bash

$ one_gadget /lib/x86_64-linux-gnu/libc.so.6

# 0x4f2c5 execve("/bin/sh", rsp+0x40, environ)

# constraints:

#   rsp & 0xf == 0

#   rcx == NULL

#

# 0x4f322 execve("/bin/sh", rsp+0x40, environ)

# constraints:

#   [rsp+0x40] == NULL

#

# 0x10a38c execve("/bin/sh", rsp+0x70, environ)

# constraints:

#   [rsp+0x70] == NULL



```

![x86_64](https://github.com/david942j/one_gadget/blob/master/examples/x86_64.png?raw=true)



#### Given BuildID

```bash

$ one_gadget -b aad7dbe330f23ea00ca63daf793b766b51aceb5d

# 0x45526 execve("/bin/sh", rsp+0x30, environ)

# constraints:

#   rax == NULL

#

# 0x4557a execve("/bin/sh", rsp+0x30, environ)

# constraints:

#   [rsp+0x30] == NULL

#

# 0xf1651 execve("/bin/sh", rsp+0x40, environ)

# constraints:

#   [rsp+0x40] == NULL

#

# 0xf24cb execve("/bin/sh", rsp+0x60, environ)

# constraints:

#   [rsp+0x60] == NULL



```

![build id](https://github.com/david942j/one_gadget/blob/master/examples/from_build_id.png?raw=true)



#### 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.



```bash

$ one_gadget /lib/x86_64-linux-gnu/libc.so.6 --near exit,mkdir

# [OneGadget] Gadgets near exit(0x43120):

# 0x4f2c5 execve("/bin/sh", rsp+0x40, environ)

# constraints:

#   rsp & 0xf == 0

#   rcx == NULL

#

# 0x4f322 execve("/bin/sh", rsp+0x40, environ)

# constraints:

#   [rsp+0x40] == NULL

#

# 0x10a38c execve("/bin/sh", rsp+0x70, environ)

# constraints:

#   [rsp+0x70] == NULL

#

# [OneGadget] Gadgets near mkdir(0x10fbb0):

# 0x10a38c execve("/bin/sh", rsp+0x70, environ)

# constraints:

#   [rsp+0x70] == NULL

#

# 0x4f322 execve("/bin/sh", rsp+0x40, environ)

# constraints:

#   [rsp+0x40] == NULL

#

# 0x4f2c5 execve("/bin/sh", rsp+0x40, environ)

# constraints:

#   rsp & 0xf == 0

#   rcx == NULL

#



```

![near](https://github.com/david942j/one_gadget/blob/master/examples/near.png?raw=true)



Regular expression is acceptable.

```bash

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

# [OneGadget] Gadgets near writev(0x1166a0):

# 1090444 324386 324293

#

# [OneGadget] Gadgets near write(0x110140):

# 1090444 324386 324293

#



```



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

```bash

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

# [OneGadget] Gadgets near exit(0x43120):

# 324293 324386 1090444

#

# [OneGadget] Gadgets near puts(0x809c0):

# 324386 324293 1090444

#

# [OneGadget] Gadgets near printf(0x64e80):

# 324386 324293 1090444

#

# [OneGadget] Gadgets near strlen(0x9dc70):

# 324386 324293 1090444

#

# [OneGadget] Gadgets near __cxa_finalize(0x43520):

# 324293 324386 1090444

#

# [OneGadget] Gadgets near __libc_start_main(0x21ab0):

# 324293 324386 1090444

#



```



#### 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.



```bash

$ one_gadget /lib/x86_64-linux-gnu/libc.so.6 --level 1

# 0x4f2c5 execve("/bin/sh", rsp+0x40, environ)

# constraints:

#   rsp & 0xf == 0

#   rcx == NULL

#

# 0x4f322 execve("/bin/sh", rsp+0x40, environ)

# constraints:

#   [rsp+0x40] == NULL

#

# 0xe569f execve("/bin/sh", r14, r12)

# constraints:

#   [r14] == NULL || r14 == NULL

#   [r12] == NULL || r12 == NULL

#

# 0xe5858 execve("/bin/sh", [rbp-0x88], [rbp-0x70])

# constraints:

#   [[rbp-0x88]] == NULL || [rbp-0x88] == NULL

#   [[rbp-0x70]] == NULL || [rbp-0x70] == NULL

#

# 0xe585f execve("/bin/sh", r10, [rbp-0x70])

# constraints:

#   [r10] == NULL || r10 == NULL

#   [[rbp-0x70]] == NULL || [rbp-0x70] == NULL

#

# 0xe5863 execve("/bin/sh", r10, rdx)

# constraints:

#   [r10] == NULL || r10 == NULL

#   [rdx] == NULL || rdx == NULL

#

# 0x10a38c execve("/bin/sh", rsp+0x70, environ)

# constraints:

#   [rsp+0x70] == NULL

#

# 0x10a398 execve("/bin/sh", rsi, [rax])

# constraints:

#   [rsi] == NULL || rsi == NULL

#   [[rax]] == NULL || [rax] == NULL



```



#### Other Architectures



##### i386

```bash

$ one_gadget /lib32/libc.so.6

# 0x3cbea execve("/bin/sh", esp+0x34, environ)

# constraints:

#   esi is the GOT address of libc

#   [esp+0x34] == NULL

#

# 0x3cbec execve("/bin/sh", esp+0x38, environ)

# constraints:

#   esi is the GOT address of libc

#   [esp+0x38] == NULL

#

# 0x3cbf0 execve("/bin/sh", esp+0x3c, environ)

# constraints:

#   esi is the GOT address of libc

#   [esp+0x3c] == NULL

#

# 0x3cbf7 execve("/bin/sh", esp+0x40, environ)

# constraints:

#   esi is the GOT address of libc

#   [esp+0x40] == NULL

#

# 0x6729f execl("/bin/sh", eax)

# constraints:

#   esi is the GOT address of libc

#   eax == NULL

#

# 0x672a0 execl("/bin/sh", [esp])

# constraints:

#   esi is the GOT address of libc

#   [esp] == NULL

#

# 0x13573e execl("/bin/sh", eax)

# constraints:

#   ebx is the GOT address of libc

#   eax == NULL

#

# 0x13573f execl("/bin/sh", [esp])

# constraints:

#   ebx is the GOT address of libc

#   [esp] == NULL



```

![i386](https://github.com/david942j/one_gadget/blob/master/examples/i386.png?raw=true)



##### AArch64

```bash

$ one_gadget spec/data/aarch64-libc-2.27.so

# 0x3f160 execve("/bin/sh", sp+0x70, environ)

# constraints:

#   address x20+0x338 is writable

#   x3 == NULL

#

# 0x3f184 execve("/bin/sh", sp+0x70, environ)

# constraints:

#   addresses x19+0x4, x20+0x338 are writable

#   [sp+0x70] == NULL

#

# 0x3f1a8 execve("/bin/sh", x21, environ)

# constraints:

#   addresses x19+0x4, x20+0x338 are writable

#   [x21] == NULL || x21 == NULL

#

# 0x63e90 execl("/bin/sh", x1)

# constraints:

#   x1 == NULL



```

![aarch64](https://github.com/david942j/one_gadget/blob/master/examples/aarch64.png?raw=true)



#### 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.



```bash

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

```



![--script](https://github.com/david942j/one_gadget/blob/master/examples/script.png?raw=true)



### In Ruby Scripts

```ruby

require 'one_gadget'

OneGadget.gadgets(file: '/lib/x86_64-linux-gnu/libc.so.6')

#=> [324293, 324386, 1090444]



# or in shorter way

one_gadget('/lib/x86_64-linux-gnu/libc.so.6', level: 1)

#=> [324293, 324386, 939679, 940120, 940127, 940131, 1090444, 1090456]



# from build id

one_gadget('b417c0ba7cc5cf06d1d1bed6652cedb9253c60d0')

#=> [324293, 324386, 1090444]



```



### To Python Lovers

```python

import subprocess

def one_gadget(filename):

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



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

#=> [324293, 324386, 1090444]



```



## 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](https://github.com/david942j/one_gadget/stargazers) :grimacing: