Zeratool: Automatic Exploit Generation

Zeratool v2.1

Automatic Exploit Generation (AEG) and remote flag capture for exploitable CTF problems

This tool uses angr to concolically analyze binaries by hooking printf and looking for unconstrained paths. These program states are then weaponized for remote code execution through pwntools and a series of script tricks. Finally the payload is tested locally then submitted to a remote CTF server to recover the flag.

Version 2.1 changes

Zeratool now supports some smart rop chain generation. During a buffer overflow Zeratool will attempt to leak a libc address and compute the base address and build a execve(/bin/sh,NULL,NULL) chain or system(/bin/sh) chain.

Installing

Zeratool has been tested on Ubuntu 16.04 through 20.04. Please install radare2 first

Usage

Zeratool is a python script which accept a binary as an argument and optionally a linked libc library, and a CTF Server connection information

[chris:~/Zeratool] zerapwn.py -h
usage: zerapwn.py [-h] [-l LIBC] [-u URL] [-p PORT] [-v] [--force_shellcode]
                  [--format_only] [--overflow_only]
                  file

positional arguments:
  file                  File to analyze

optional arguments:
  -h, --help            show this help message and exit
  -l LIBC, --libc LIBC  libc to use
  -u URL, --url URL     Remote URL to pwn
  -p PORT, --port PORT  Remote port to pwn
  -v, --verbose         Verbose mode
  --force_shellcode     Set overflow pwn mode to point to shellcode
  --format_only         Only run format strings check
  --overflow_only       Only run overflow check

Exploit Types

Zeratool is designed around weaponizing buffer overflows and format string vulnerabilities and currently supports a couple types:

• Buffer Overflow
  • Point program counter to win function
  • Point program counter to shellcode
  • Point program counter to rop chain
    • Rop chains will attempt to leak a libc function
    • Rop chains will then execve(/bin/sh) or system(/bin/sh)
• Format String
  • Point GOT entry to win function
  • Point GOT entry to shellcode

Examples

Checkout the samples.sh file. The file contains several examples of Zeratool automatically solving exploitable CTF problems.

#!/bin/bash
# Buffer Overflows with win functions
zerapwn.py tests/bin/bof_win_32
zerapwn.py tests/bin/bof_win_64
# Buffer Overflows with ropping
zerapwn.py tests/bin/bof_nx_32
zerapwn.py tests/bin/bof_nx_64
# Buffer Overflow with ropping and libc leak
zerapwn.py tests/bin/bof_nx_64 -l tests/bin/libc.so.6_amd64

#Format string leak
zerapwn.py tests/bin/read_stack_32
zerapwn.py tests/bin/read_stack_64
#Format string point to win function
zerapwn.py challenges/medium_format
#Format string point to shellcode
#zerapwn.py challenges/hard_format #This one sometimes needs to be run twice

# Buffer overflow point to shellcode
# Turn off aslr 
# echo 0 | sudo tee /proc/sys/kernel/randomize_va_space
zerapwn.py tests/bin/bof_32 --force_shellcode
zerapwn.py tests/bin/bof_64 --force_shellcode

Long Asciinema with Three Solves

Run the tests!

Tox and Pytest are used to verify that Zeratool is working correctly.

FAQ

Q. Why doesn't Zeratool work against my simple exploitable?

A. Zeratool is held together by scotch tape and dreams.

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