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Angr - Beispiele

Reading time: 16 minutes

Codes stammen von https://github.com/jakespringer/angr_ctf

Eingabe, um die Adresse zu erreichen (die Adresse anzeigend)

import angr
import sys

def main(argv):
path_to_binary = argv[1]  # :string
project = angr.Project(path_to_binary)

# Start in main()
initial_state = project.factory.entry_state()
# Start simulation
simulation = project.factory.simgr(initial_state)

# Find the way yo reach the good address
good_address = 0x804867d

# Avoiding this address
avoid_address = 0x080485A8
simulation.explore(find=good_address, avoid=avoid_address)

# If found a way to reach the address
if simulation.found:
solution_state = simulation.found[0]

# Print the string that Angr wrote to stdin to follow solution_state
print(solution_state.posix.dumps(sys.stdin.fileno()))
else:
raise Exception('Could not find the solution')

if __name__ == '__main__':
main(sys.argv)

Eingabe zur Erreichung der Adresse (Druckanzeigen anzeigen)

# If you don't know the address you want to recah, but you know it's printing something
# You can also indicate that info

import angr
import sys

def main(argv):
path_to_binary = argv[1]
project = angr.Project(path_to_binary)
initial_state = project.factory.entry_state()
simulation = project.factory.simgr(initial_state)

def is_successful(state):
#Successful print
stdout_output = state.posix.dumps(sys.stdout.fileno())
return b'Good Job.' in stdout_output

def should_abort(state):
#Avoid this print
stdout_output = state.posix.dumps(sys.stdout.fileno())
return b'Try again.' in stdout_output

simulation.explore(find=is_successful, avoid=should_abort)

if simulation.found:
solution_state = simulation.found[0]
print(solution_state.posix.dumps(sys.stdin.fileno()))
else:
raise Exception('Could not find the solution')

if __name__ == '__main__':
main(sys.argv)

Registrierungswerte

# Angr doesn't currently support reading multiple things with scanf (Ex:
# scanf("%u %u).) You will have to tell the simulation engine to begin the
# program after scanf is called and manually inject the symbols into registers.

import angr
import claripy
import sys

def main(argv):
path_to_binary = argv[1]
project = angr.Project(path_to_binary)

# Address were you want to indicate the relation BitVector - registries
start_address = 0x80488d1
initial_state = project.factory.blank_state(addr=start_address)


# Create Bit Vectors
password0_size_in_bits = 32  # :integer
password0 = claripy.BVS('password0', password0_size_in_bits)

password1_size_in_bits = 32  # :integer
password1 = claripy.BVS('password1', password1_size_in_bits)

password2_size_in_bits = 32  # :integer
password2 = claripy.BVS('password2', password2_size_in_bits)

# Relate it Vectors with the registriy values you are interested in to reach an address
initial_state.regs.eax = password0
initial_state.regs.ebx = password1
initial_state.regs.edx = password2

simulation = project.factory.simgr(initial_state)

def is_successful(state):
stdout_output = state.posix.dumps(sys.stdout.fileno())
return 'Good Job.'.encode() in stdout_output

def should_abort(state):
stdout_output = state.posix.dumps(sys.stdout.fileno())
return 'Try again.'.encode() in stdout_output

simulation.explore(find=is_successful, avoid=should_abort)

if simulation.found:
solution_state = simulation.found[0]

solution0 = solution_state.solver.eval(password0)
solution1 = solution_state.solver.eval(password1)
solution2 = solution_state.solver.eval(password2)

# Aggregate and format the solutions you computed above, and then print
# the full string. Pay attention to the order of the integers, and the
# expected base (decimal, octal, hexadecimal, etc).
solution = ' '.join(map('{:x}'.format, [ solution0, solution1, solution2 ]))  # :string
print(solution)
else:
raise Exception('Could not find the solution')

if __name__ == '__main__':
main(sys.argv)

Stack-Werte

# Put bit vectors in th stack to find out the vallue that stack position need to
# have to reach a rogram flow

import angr
import claripy
import sys

def main(argv):
path_to_binary = argv[1]
project = angr.Project(path_to_binary)

# Go to some address after the scanf where values have already being set in the stack
start_address = 0x8048697
initial_state = project.factory.blank_state(addr=start_address)

# Since we are starting after scanf, we are skipping this stack construction
# step. To make up for this, we need to construct the stack ourselves. Let us
# start by initializing ebp in the exact same way the program does.
initial_state.regs.ebp = initial_state.regs.esp

# In this case scanf("%u %u") is used, so 2 BVS are going to be needed
password0 = claripy.BVS('password0', 32)
password1 = claripy.BVS('password1', 32)

# Now, in the address were you have stopped, check were are the scanf values saved
# Then, substrack form the esp registry the needing padding to get to the
# part of the stack were the scanf values are being saved and push the BVS
# (see the image below to understan this -8)
padding_length_in_bytes = 8  # :integer
initial_state.regs.esp -= padding_length_in_bytes

initial_state.stack_push(password0)
initial_state.stack_push(password1)

simulation = project.factory.simgr(initial_state)

def is_successful(state):
stdout_output = state.posix.dumps(sys.stdout.fileno())
return 'Good Job.'.encode() in stdout_output

def should_abort(state):
stdout_output = state.posix.dumps(sys.stdout.fileno())
return 'Try again.'.encode() in stdout_output

simulation.explore(find=is_successful, avoid=should_abort)

if simulation.found:
solution_state = simulation.found[0]

solution0 = solution_state.solver.eval(password0)
solution1 = solution_state.solver.eval(password1)

solution = ' '.join(map(str, [ solution0, solution1 ]))
print(solution)
else:
raise Exception('Could not find the solution')

if __name__ == '__main__':
main(sys.argv)

In diesem Szenario wurde die Eingabe mit scanf("%u %u") entgegengenommen und der Wert "1 1" wurde angegeben, sodass die Werte 0x00000001 vom Benutzereingang stammen. Sie können sehen, wie diese Werte bei $ebp - 8 beginnen. Daher haben wir im Code 8 Bytes von $esp subtrahiert (da zu diesem Zeitpunkt $ebp und $esp den gleichen Wert hatten) und dann haben wir die BVS gepusht.

Statische Speicherwerte (Globale Variablen)

import angr
import claripy
import sys

def main(argv):
path_to_binary = argv[1]
project = angr.Project(path_to_binary)

#Get an address after the scanf. Once the input has already being saved in the memory positions
start_address = 0x8048606
initial_state = project.factory.blank_state(addr=start_address)

# The binary is calling scanf("%8s %8s %8s %8s").
# So we need 4 BVS of size 8*8
password0 = claripy.BVS('password0', 8*8)
password1 = claripy.BVS('password1', 8*8)
password2 = claripy.BVS('password2', 8*8)
password3 = claripy.BVS('password3', 8*8)

# Write the symbolic BVS in the memory positions
password0_address = 0xa29faa0
initial_state.memory.store(password0_address, password0)
password1_address = 0xa29faa8
initial_state.memory.store(password1_address, password1)
password2_address = 0xa29fab0
initial_state.memory.store(password2_address, password2)
password3_address = 0xa29fab8
initial_state.memory.store(password3_address, password3)

simulation = project.factory.simgr(initial_state)

def is_successful(state):
stdout_output = state.posix.dumps(sys.stdout.fileno())
return 'Good Job.'.encode() in stdout_output

def should_abort(state):
stdout_output = state.posix.dumps(sys.stdout.fileno())
return 'Try again.'.encode() in stdout_output

simulation.explore(find=is_successful, avoid=should_abort)

if simulation.found:
solution_state = simulation.found[0]

# Get the values the memory addresses should store
solution0 = solution_state.solver.eval(password0,cast_to=bytes).decode()
solution1 = solution_state.solver.eval(password1,cast_to=bytes).decode()
solution2 = solution_state.solver.eval(password2,cast_to=bytes).decode()
solution3 = solution_state.solver.eval(password3,cast_to=bytes).decode()

solution = ' '.join([ solution0, solution1, solution2, solution3 ])

print(solution)
else:
raise Exception('Could not find the solution')

if __name__ == '__main__':
main(sys.argv)

Dynamische Speicherwerte (Malloc)

import angr
import claripy
import sys

def main(argv):
path_to_binary = argv[1]
project = angr.Project(path_to_binary)

# Get address after scanf
start_address = 0x804869e
initial_state = project.factory.blank_state(addr=start_address)

# The binary is calling scanf("%8s %8s") so 2 BVS are needed.
password0 = claripy.BVS('password0', 8*8)
password1 = claripy.BVS('password0', 8*8)

# Find a coupble of addresses that aren't used by the binary (like 0x4444444 & 0x4444454)
# The address generated by mallosc is going to be saved in some address
# Then, make that address point to the fake heap addresses were the BVS are going to be saved
fake_heap_address0 = 0x4444444
pointer_to_malloc_memory_address0 = 0xa79a118
initial_state.memory.store(pointer_to_malloc_memory_address0, fake_heap_address0, endness=project.arch.memory_endness)
fake_heap_address1 = 0x4444454
pointer_to_malloc_memory_address1 = 0xa79a120
initial_state.memory.store(pointer_to_malloc_memory_address1, fake_heap_address1, endness=project.arch.memory_endness)

# Save the VBS in the new fake heap addresses created
initial_state.memory.store(fake_heap_address0, password0)
initial_state.memory.store(fake_heap_address1, password1)

simulation = project.factory.simgr(initial_state)

def is_successful(state):
stdout_output = state.posix.dumps(sys.stdout.fileno())
return 'Good Job.'.encode() in stdout_output

def should_abort(state):
stdout_output = state.posix.dumps(sys.stdout.fileno())
return 'Try again.'.encode() in stdout_output

simulation.explore(find=is_successful, avoid=should_abort)

if simulation.found:
solution_state = simulation.found[0]

solution0 = solution_state.solver.eval(password0,cast_to=bytes).decode()
solution1 = solution_state.solver.eval(password1,cast_to=bytes).decode()

solution = ' '.join([ solution0, solution1 ])

print(solution)
else:
raise Exception('Could not find the solution')

if __name__ == '__main__':
main(sys.argv)

Dateisimulation

#In this challenge a password is read from a file and we want to simulate its content

import angr
import claripy
import sys

def main(argv):
path_to_binary = argv[1]
project = angr.Project(path_to_binary)

# Get an address just before opening the file with th simbolic content
# Or at least when the file is not going to suffer more changes before being read
start_address = 0x80488db
initial_state = project.factory.blank_state(addr=start_address)

# Specify the filena that is going to open
# Note that in theory, the filename could be symbolic.
filename = 'WCEXPXBW.txt'
symbolic_file_size_bytes = 64

# Create a BV which is going to be the content of the simbolic file
password = claripy.BVS('password', symbolic_file_size_bytes * 8)

# Create the file simulation with the simbolic content
password_file = angr.storage.SimFile(filename, content=password)

# Add the symbolic file we created to the symbolic filesystem.
initial_state.fs.insert(filename, password_file)

simulation = project.factory.simgr(initial_state)

def is_successful(state):
stdout_output = state.posix.dumps(sys.stdout.fileno())
return 'Good Job.'.encode() in stdout_output

def should_abort(state):
stdout_output = state.posix.dumps(sys.stdout.fileno())
return 'Try again.'.encode() in stdout_output

simulation.explore(find=is_successful, avoid=should_abort)

if simulation.found:
solution_state = simulation.found[0]

solution = solution_state.solver.eval(password,cast_to=bytes).decode()

print(solution)
else:
raise Exception('Could not find the solution')

if __name__ == '__main__':
main(sys.argv)

  # Hallo Welt, mein Name ist John.
  # ^                       ^
  # ^ Adresse 0             ^ Adresse 24 (zähle die Anzahl der Zeichen)
  # Um dies im Speicher darzustellen, möchten wir den String an
  # den Anfang der Datei schreiben:
  #
  # hello_txt_contents = claripy.BVV('Hallo Welt, mein Name ist John.', 30*8)
  #
  # Vielleicht möchten wir dann John durch eine
  # symbolische Variable ersetzen. Wir würden aufrufen:
  #
  # name_bitvector = claripy.BVS('symbolic_name', 4*8)
  #
  # Dann, nachdem das Programm fopen('hello.txt', 'r') aufruft und dann
  # fread(buffer, sizeof(char), 30, hello_txt_file) aufruft, würde der Puffer
  # den String aus der Datei enthalten, außer vier symbolischen Bytes, wo der Name
  # gespeichert wäre.
  # (!)

Anwenden von Einschränkungen

# After perform some complex poperations to the input the program checks
# char by char the password against another password saved, like in the snippet:
#
# #define REFERENCE_PASSWORD = "AABBCCDDEEFFGGHH";
# int check_equals_AABBCCDDEEFFGGHH(char* to_check, size_t length) {
#   uint32_t num_correct = 0;
#   for (int i=0; i<length; ++i) {
#     if (to_check[i] == REFERENCE_PASSWORD[i]) {
#       num_correct += 1;
#     }
#   }
#   return num_correct == length;
# }
#
# ...
#
# char* input = user_input();
# char* encrypted_input = complex_function(input);
# if (check_equals_AABBCCDDEEFFGGHH(encrypted_input, 16)) {
#   puts("Good Job.");
# } else {
#   puts("Try again.");
# }
#
# The function checks if *to_check == "AABBCCDDEEFFGGHH". This is very RAM consumming
# as the computer needs to branch every time the if statement in the loop was called (16
# times), resulting in 2^16 = 65,536 branches, which will take too long of a
# time to evaluate for our needs.

import angr
import claripy
import sys

def main(argv):
path_to_binary = argv[1]
project = angr.Project(path_to_binary)

initial_state = project.factory.entry_state()

simulation = project.factory.simgr(initial_state)

# Get an address to check after the complex function and before the "easy compare" operation
address_to_check_constraint = 0x8048671
simulation.explore(find=address_to_check_constraint)


if simulation.found:
solution_state = simulation.found[0]

# Find were the input that is going to be compared is saved in memory
constrained_parameter_address = 0x804a050
constrained_parameter_size_bytes = 16
# Set the bitvector
constrained_parameter_bitvector = solution_state.memory.load(
constrained_parameter_address,
constrained_parameter_size_bytes
)

# Indicate angr that this BV at this point needs to be equal to the password
constrained_parameter_desired_value = 'BWYRUBQCMVSBRGFU'.encode()
solution_state.add_constraints(constrained_parameter_bitvector == constrained_parameter_desired_value)

print(solution_state.posix.dumps(sys.stdin.fileno()))
else:
raise Exception('Could not find the solution')

if __name__ == '__main__':
main(sys.argv)

Simulation Managers

Einige Simulation Managers können nützlicher sein als andere. Im vorherigen Beispiel gab es ein Problem, da viele nützliche Zweige erstellt wurden. Hier wird die veritesting-Technik diese zusammenführen und eine Lösung finden.
Dieser Simulation Manager kann auch aktiviert werden mit: simulation = project.factory.simgr(initial_state, veritesting=True)

import angr
import claripy
import sys

def main(argv):
path_to_binary = argv[1]
project = angr.Project(path_to_binary)

initial_state = project.factory.entry_state()

simulation = project.factory.simgr(initial_state)
# Set simulation technique
simulation.use_technique(angr.exploration_techniques.Veritesting())


def is_successful(state):
stdout_output = state.posix.dumps(sys.stdout.fileno())

return 'Good Job.'.encode() in stdout_output  # :boolean

def should_abort(state):
stdout_output = state.posix.dumps(sys.stdout.fileno())
return 'Try again.'.encode() in stdout_output  # :boolean

simulation.explore(find=is_successful, avoid=should_abort)

if simulation.found:
solution_state = simulation.found[0]
print(solution_state.posix.dumps(sys.stdin.fileno()))
else:
raise Exception('Could not find the solution')


if __name__ == '__main__':
main(sys.argv)

Hooking/Bypassing einen Aufruf zu einer Funktion

# This level performs the following computations:
#
# 1. Get 16 bytes of user input and encrypt it.
# 2. Save the result of check_equals_AABBCCDDEEFFGGHH (or similar)
# 3. Get another 16 bytes from the user and encrypt it.
# 4. Check that it's equal to a predefined password.
#
# The ONLY part of this program that we have to worry about is #2. We will be
# replacing the call to check_equals_ with our own version, using a hook, since
# check_equals_ will run too slowly otherwise.

import angr
import claripy
import sys

def main(argv):
path_to_binary = argv[1]
project = angr.Project(path_to_binary)

initial_state = project.factory.entry_state()

# Hook the address of the call to hook indicating th length of the instruction (of the call)
check_equals_called_address = 0x80486b8
instruction_to_skip_length = 5
@project.hook(check_equals_called_address, length=instruction_to_skip_length)
def skip_check_equals_(state):
#Load the input of the function reading direcly the memory
user_input_buffer_address = 0x804a054
user_input_buffer_length = 16
user_input_string = state.memory.load(
user_input_buffer_address,
user_input_buffer_length
)

# Create a simbolic IF that if the loaded string frommemory is the expected
# return True (1) if not returns False (0) in eax
check_against_string = 'XKSPZSJKJYQCQXZV'.encode() # :string

state.regs.eax = claripy.If(
user_input_string == check_against_string,
claripy.BVV(1, 32),
claripy.BVV(0, 32)
)

simulation = project.factory.simgr(initial_state)

def is_successful(state):
stdout_output = state.posix.dumps(sys.stdout.fileno())
return 'Good Job.'.encode() in stdout_output

def should_abort(state):
stdout_output = state.posix.dumps(sys.stdout.fileno())
return 'Try again.'.encode() in stdout_output

simulation.explore(find=is_successful, avoid=should_abort)

if simulation.found:
solution_state = simulation.found[0]
solution = solution_state.posix.dumps(sys.stdin.fileno()).decode()
print(solution)
else:
raise Exception('Could not find the solution')

if __name__ == '__main__':
main(sys.argv)

Eine Funktion hooken / Simprocedure

# Hook to the function called check_equals_WQNDNKKWAWOLXBAC

import angr
import claripy
import sys

def main(argv):
path_to_binary = argv[1]
project = angr.Project(path_to_binary)

initial_state = project.factory.entry_state()

# Define a class and a tun method to hook completelly a function
class ReplacementCheckEquals(angr.SimProcedure):
# This C code:
#
# int add_if_positive(int a, int b) {
#   if (a >= 0 && b >= 0) return a + b;
#   else return 0;
# }
#
# could be simulated with python:
#
# class ReplacementAddIfPositive(angr.SimProcedure):
#   def run(self, a, b):
#     if a >= 0 and b >=0:
#       return a + b
#     else:
#       return 0
#
# run(...) receives the params of the hooked function
def run(self, to_check, length):
user_input_buffer_address = to_check
user_input_buffer_length = length

# Read the data from the memory address given to the function
user_input_string = self.state.memory.load(
user_input_buffer_address,
user_input_buffer_length
)

check_against_string = 'WQNDNKKWAWOLXBAC'.encode()

# Return 1 if equals to the string, 0 otherways
return claripy.If(
user_input_string == check_against_string,
claripy.BVV(1, 32),
claripy.BVV(0, 32)
)


# Hook the check_equals symbol. Angr automatically looks up the address
# associated with the symbol. Alternatively, you can use 'hook' instead
# of 'hook_symbol' and specify the address of the function. To find the
# correct symbol, disassemble the binary.
# (!)
check_equals_symbol = 'check_equals_WQNDNKKWAWOLXBAC' # :string
project.hook_symbol(check_equals_symbol, ReplacementCheckEquals())

simulation = project.factory.simgr(initial_state)

def is_successful(state):
stdout_output = state.posix.dumps(sys.stdout.fileno())
return 'Good Job.'.encode() in stdout_output

def should_abort(state):
stdout_output = state.posix.dumps(sys.stdout.fileno())
return 'Try again.'.encode() in stdout_output

simulation.explore(find=is_successful, avoid=should_abort)

if simulation.found:
solution_state = simulation.found[0]

solution = solution_state.posix.dumps(sys.stdin.fileno()).decode()
print(solution)
else:
raise Exception('Could not find the solution')

if __name__ == '__main__':
main(sys.argv)

Simuliere scanf mit mehreren Parametern

# This time, the solution involves simply replacing scanf with our own version,
# since Angr does not support requesting multiple parameters with scanf.

import angr
import claripy
import sys

def main(argv):
path_to_binary = argv[1]
project = angr.Project(path_to_binary)

initial_state = project.factory.entry_state()

class ReplacementScanf(angr.SimProcedure):
# The code uses: 'scanf("%u %u", ...)'
def run(self, format_string, param0, param1):
scanf0 = claripy.BVS('scanf0', 32)
scanf1 = claripy.BVS('scanf1', 32)

# Get the addresses from the params and store the BVS in memory
scanf0_address = param0
self.state.memory.store(scanf0_address, scanf0, endness=project.arch.memory_endness)
scanf1_address = param1
self.state.memory.store(scanf1_address, scanf1, endness=project.arch.memory_endness)

# Now, we want to 'set aside' references to our symbolic values in the
# globals plugin included by default with a state. You will need to
# store multiple bitvectors. You can either use a list, tuple, or multiple
# keys to reference the different bitvectors.
self.state.globals['solutions'] = (scanf0, scanf1)

scanf_symbol = '__isoc99_scanf'
project.hook_symbol(scanf_symbol, ReplacementScanf())

simulation = project.factory.simgr(initial_state)

def is_successful(state):
stdout_output = state.posix.dumps(sys.stdout.fileno())
return 'Good Job.'.encode() in stdout_output

def should_abort(state):
stdout_output = state.posix.dumps(sys.stdout.fileno())
return 'Try again.'.encode() in stdout_output

simulation.explore(find=is_successful, avoid=should_abort)

if simulation.found:
solution_state = simulation.found[0]

# Grab whatever you set aside in the globals dict.
stored_solutions = solution_state.globals['solutions']
solution = ' '.join(map(str, map(solution_state.solver.eval, stored_solutions)))

print(solution)
else:
raise Exception('Could not find the solution')

if __name__ == '__main__':
main(sys.argv)

Statische Binaries

# This challenge is the exact same as the first challenge, except that it was
# compiled as a static binary. Normally, Angr automatically replaces standard
# library functions with SimProcedures that work much more quickly.
#
# To solve the challenge, manually hook any standard library c functions that
# are used. Then, ensure that you begin the execution at the beginning of the
# main function. Do not use entry_state.
#
# Here are a few SimProcedures Angr has already written for you. They implement
# standard library functions. You will not need all of them:
# angr.SIM_PROCEDURES['libc']['malloc']
# angr.SIM_PROCEDURES['libc']['fopen']
# angr.SIM_PROCEDURES['libc']['fclose']
# angr.SIM_PROCEDURES['libc']['fwrite']
# angr.SIM_PROCEDURES['libc']['getchar']
# angr.SIM_PROCEDURES['libc']['strncmp']
# angr.SIM_PROCEDURES['libc']['strcmp']
# angr.SIM_PROCEDURES['libc']['scanf']
# angr.SIM_PROCEDURES['libc']['printf']
# angr.SIM_PROCEDURES['libc']['puts']
# angr.SIM_PROCEDURES['libc']['exit']
#
# As a reminder, you can hook functions with something similar to:
# project.hook(malloc_address, angr.SIM_PROCEDURES['libc']['malloc']())
#
# There are many more, see:
# https://github.com/angr/angr/tree/master/angr/procedures/libc

import angr
import sys

def main(argv):
path_to_binary = argv[1]
project = angr.Project(path_to_binary)

initial_state = project.factory.entry_state()

#Find the addresses were the lib functions are loaded in the binary
#For example you could find: call   0x804ed80 <__isoc99_scanf>
project.hook(0x804ed40, angr.SIM_PROCEDURES['libc']['printf']())
project.hook(0x804ed80, angr.SIM_PROCEDURES['libc']['scanf']())
project.hook(0x804f350, angr.SIM_PROCEDURES['libc']['puts']())
project.hook(0x8048d10, angr.SIM_PROCEDURES['glibc']['__libc_start_main']())

simulation = project.factory.simgr(initial_state)

def is_successful(state):
stdout_output = state.posix.dumps(sys.stdout.fileno())
return 'Good Job.'.encode() in stdout_output  # :boolean

def should_abort(state):
stdout_output = state.posix.dumps(sys.stdout.fileno())
return 'Try again.'.encode() in stdout_output  # :boolean

simulation.explore(find=is_successful, avoid=should_abort)

if simulation.found:
solution_state = simulation.found[0]
print(solution_state.posix.dumps(sys.stdin.fileno()).decode())
else:
raise Exception('Could not find the solution')

if __name__ == '__main__':
main(sys.argv)