Tags: angr re
Rating:
# Foobar CTF - Formless
The binary asks the user to input the flag and then performs a check it. The binary then prints out one of two messages depending on if you succeeded our failed.
```
00001a6a if (check(&var_46, strlen(&var_46)) == 0)
00001a68 {
00001a8a printf("Conquer the path ahead of you");
00001a89 }
00001a76 else
00001a76 {
00001a76 printf("Empty your mind, be more formles…");
00001a75 }
```
Due to only having two paths, this problem should be fairly easy to model and solve in angr. We load the binary with the angr ``factory.entry_state`` and then execute a simulation, checking the two paths discovered and the input neccessary to produce the output at each path.
```python
import angr, logging
logging.getLogger('angr').setLevel('CRITICAL')
print("[+] Loading Angr Project for Formless Challenge")
p = angr.Project('./chall',main_opts={"base_addr": 0x400000})
state = p.factory.entry_state()
sm = p.factory.simulation_manager(state)
sm.run()
print("\t--0")
print("\t[+] Deadend 0: Input = %s" %sm.deadended[0].posix.dumps(0))
print("\t[+] Deadend 0: Output = %s" %sm.deadended[0].posix.dumps(1))
print("\t--1")
print("\t[+] Deadend 1: Input = %s" %sm.deadended[1].posix.dumps(0))
print("\t[+] Deadend 1: Output = %s" %sm.deadended[1].posix.dumps(1))
```
The result shows the path with the flag as the second deadend state input: ``GLUG{bE_W@tER_my_FriEnD}``
```
[+] Loading Angr Project for Formless Challenge
--0
[+] Deadend 0: Input = b'\x00\x00\x00\x00...'
[+] Deadend 0: Output = b'Empty your mind, be more formless'
--1
[+] Deadend 1: Input = b'GLUG{bE_W@tER_my_FriEnD}\x00\x00...'
[+] Deadend 1: Output = b'Conquer the path ahead of you'
```
