Exploit Development Loop

Write exploits iteratively — run, observe, fix, repeat until the flag drops.

Workflow

1. Understand the vulnerability — Read challenge source/binary analysis first
2. Write initial exploit — Start simple, add complexity as needed
3. Test against target — Run locally first, then remote
4. Debug failures — Read output carefully, add debug prints, check assumptions
5. Iterate — Fix and re-run until flag captured
6. Clean up — Save working exploit as solve.py, flag to flag.txt

Exploit Templates

Binary Exploitation (pwntools)

#!/usr/bin/env python3
from pwn import *

context.binary = elf = ELF('./binary')
# context.log_level = 'debug'

def conn():
    if args.REMOTE:
        return remote('HOST', PORT)
    return process('./binary')

io = conn()

# === EXPLOIT HERE ===

io.interactive()

Web Exploitation (requests)

#!/usr/bin/env python3
import requests
import sys

TARGET = sys.argv[1] if len(sys.argv) > 1 else 'http://localhost:8080'
s = requests.Session()

# === EXPLOIT HERE ===

print(f"FLAG: {flag}")

Crypto Solve Script

#!/usr/bin/env python3
from Crypto.Util.number import *
from pwn import *

# === GIVEN VALUES ===

# === SOLVE ===

flag = long_to_bytes(m)
print(f"FLAG: {flag.decode()}")

Pwntools Remote Interaction

#!/usr/bin/env python3
from pwn import *

io = remote('HOST', PORT)

# Read until prompt
io.recvuntil(b'> ')

# Send payload
io.sendline(payload)

# Get response
response = io.recvline()
print(f"Response: {response}")

# Interactive mode for shell
io.interactive()

Debug Tips

• Use context.log_level = 'debug' for full pwntools traffic
• Add print(f"[*] payload: {payload.hex()}") before sends
• Use io.recv(timeout=2) to see unexpected output
• Check io.can_recv() before blocking reads
• Use gdb.attach(io) for local debugging with breakpoints
• For web: print(r.status_code, r.text[:500]) after every request

Common Pitfalls

• Wrong endianness: Use p64() for little-endian, p64(val, endian='big') for big
• Newline issues: sendline() adds \n, send() doesn't — know which the server expects
• Timing: Add sleep(0.5) between sends if server is slow
• Encoding: Web payloads may need URL encoding, base64, or hex
• Stack alignment: x86-64 needs 16-byte alignment — add extra ret gadget
• Python 2 vs 3: pwntools works with bytes in Python 3 — use b"string" not "string"

Iteration Pattern

1. Write exploit → run → "Connection refused"
   Fix: Check host/port, is service up?

2. Write exploit → run → "EOF in recv"
   Fix: Server closed connection — payload crashed it. Check offsets.

3. Write exploit → run → wrong output
   Fix: Add debug prints, check each step's output matches expectation.

4. Write exploit → run → "flag{...}"
   Done! Save to flag.txt

Target

$ARGUMENTS