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add custom netcat tutorial
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‎README.md

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@@ -71,6 +71,7 @@ This is a repository of all the tutorials of [The Python Code](https://www.thepy
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- [How to Check Password Strength with Python](https://thepythoncode.com/article/test-password-strength-with-python). ([code](ethical-hacking/checking-password-strength))
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- [How to Perform Reverse DNS Lookups Using Python](https://thepythoncode.com/article/reverse-dns-lookup-with-python). ([code](ethical-hacking/reverse-dns-lookup))
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- [How to Make a Clickjacking Vulnerability Scanner in Python](https://thepythoncode.com/article/make-a-clickjacking-vulnerability-scanner-with-python). ([code](ethical-hacking/clickjacking-scanner))
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- [How to Build a Custom NetCat with Python](https://thepythoncode.com/article/create-a-custom-netcat-in-python). ([code](ethical-hacking/custom-netcat/))
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- ### [Machine Learning](https://www.thepythoncode.com/topic/machine-learning)
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- ### [Natural Language Processing](https://www.thepythoncode.com/topic/nlp)

‎ethical-hacking/custom-netcat/README.md

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# [How to Build a Custom NetCat with Python](https://thepythoncode.com/article/create-a-custom-netcat-in-python)

‎ethical-hacking/custom-netcat/netcat.py

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import sys, socket, getopt, threading, subprocess, signal, time
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class NetCat:
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def __init__(self, target, port):
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self.listen = False
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self.command = False
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self.upload = False
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self.execute = ""
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self.target = target
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self.upload_destination = ""
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self.port = port
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self.running = True
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self.threads = []
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def signal_handler(self, signum, frame):
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print('\n[*] User requested an interrupt. Exiting gracefully.')
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self.running = False
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time.sleep(0.5)
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sys.exit(0)
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def run_command(self, cmd):
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cmd = cmd.rstrip()
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try:
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output = subprocess.check_output(cmd, stderr=subprocess.STDOUT, shell=True)
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except subprocess.CalledProcessError as e:
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output = e.output
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except Exception as e:
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output = str(e).encode()
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return output
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def handle_client(self, client_socket):
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try:
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if len(self.upload_destination):
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file_buffer = ""
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while self.running:
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try:
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data = client_socket.recv(1024)
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if not data:
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break
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else:
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file_buffer += data.decode('utf-8')
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except (ConnectionResetError, BrokenPipeError) as e:
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print(f"[!] Connection error during upload: {str(e)}")
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break
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except Exception as e:
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print(f"[!] Error receiving data: {str(e)}")
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break
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try:
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with open(self.upload_destination, "wb") as file_descriptor:
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file_descriptor.write(file_buffer.encode('utf-8'))
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try:
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client_socket.send(
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f"Successfully saved file to {self.upload_destination}\r\n".encode('utf-8'))
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except (BrokenPipeError, ConnectionResetError):
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print("[!] Couldn't send success message - connection lost")
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except OSError as e:
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print(f"[!] File operation failed: {str(e)}")
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try:
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client_socket.send(
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f"Failed to save file to {self.upload_destination}\r\n".encode('utf-8'))
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except (BrokenPipeError, ConnectionResetError):
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print("[!] Couldn't send error message - connection lost")
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if len(self.execute) and self.running:
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try:
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output = self.run_command(self.execute)
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client_socket.send(output)
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except (BrokenPipeError, ConnectionResetError):
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print("[!] Couldn't send command output - connection lost")
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except Exception as e:
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print(f"[!] Error executing command: {str(e)}")
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if self.command:
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while self.running:
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try:
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# Send prompt
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client_socket.send(b"<Target:#> ")
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# Receive command
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cmd_buffer = b''
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while b"\n" not in cmd_buffer and self.running:
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try:
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data = client_socket.recv(1024)
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if not data:
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raise ConnectionResetError("No data received")
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cmd_buffer += data
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except socket.timeout:
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continue
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except (ConnectionResetError, BrokenPipeError):
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raise
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if not self.running:
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break
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# Execute command and send response
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try:
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cmd = cmd_buffer.decode().strip()
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if cmd.lower() in ['exit', 'quit']:
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print("[*] User requested exit")
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break
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output = self.run_command(cmd)
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if output:
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client_socket.send(output + b"\n")
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else:
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client_socket.send(b"Command completed without output\n")
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except (BrokenPipeError, ConnectionResetError):
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print("[!] Connection lost while sending response")
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break
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except Exception as e:
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error_msg = f"Error executing command: {str(e)}\n"
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try:
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client_socket.send(error_msg.encode())
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except:
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break
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except ConnectionResetError:
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print("[!] Connection reset by peer")
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break
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except BrokenPipeError:
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print("[!] Broken pipe - connection lost")
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break
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except Exception as e:
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print(f"[!] Error in command loop: {str(e)}")
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break
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except Exception as e:
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print(f"[!] Exception in handle_client: {str(e)}")
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finally:
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try:
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client_socket.close()
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print("[*] Client connection closed")
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except:
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pass
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def server_loop(self):
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server = None
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try:
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if not len(self.target):
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self.target = "0.0.0.0"
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server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
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server.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
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server.bind((self.target, self.port))
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server.listen(5)
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print(f"[*] Listening on {self.target}:{self.port}")
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server.settimeout(1.0)
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while self.running:
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try:
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client_socket, addr = server.accept()
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print(f"[*] Accepted connection from {addr[0]}:{addr[1]}")
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client_thread = threading.Thread(
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target=self.handle_client,
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args=(client_socket,)
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)
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client_thread.daemon = True
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self.threads.append(client_thread)
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client_thread.start()
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except socket.timeout:
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continue
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except Exception as e:
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if self.running:
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print(f"[!] Exception in server_loop: {str(e)}")
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break
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except Exception as e:
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print(f"[!] Failed to create server: {str(e)}")
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finally:
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if server:
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try:
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server.close()
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print("[*] Server socket closed")
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except:
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pass
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for thread in self.threads:
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try:
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thread.join(timeout=1.0)
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except threading.ThreadError:
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pass
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def client_sender(self, buffer):
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client = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
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try:
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print(f"[*] Connecting to {self.target}:{self.port}")
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client.connect((self.target, self.port))
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if len(buffer):
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try:
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client.send(buffer.encode('utf-8'))
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except (BrokenPipeError, ConnectionResetError):
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print("[!] Failed to send initial buffer - connection lost")
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return
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while self.running:
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try:
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# Receive response from server
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recv_len = 1
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response = b''
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while recv_len:
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data = client.recv(4096)
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recv_len = len(data)
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response += data
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if recv_len < 4096:
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break
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if response:
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print(response.decode('utf-8'), end='')
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# Get next command
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buffer = input()
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if not self.running:
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break
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if buffer.lower() in ['exit', 'quit']:
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break
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buffer += "\n"
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try:
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client.send(buffer.encode('utf-8'))
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except (BrokenPipeError, ConnectionResetError):
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print("\n[!] Failed to send data - connection lost")
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break
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except ConnectionResetError:
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print("\n[!] Connection reset by peer")
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break
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except BrokenPipeError:
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print("\n[!] Broken pipe - connection lost")
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break
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except EOFError:
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print("\n[!] EOF detected - exiting")
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break
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except Exception as e:
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print(f"\n[!] Exception in client loop: {str(e)}")
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break
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except socket.error as exc:
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print("\n[!] Exception! Exiting.")
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print(f"[!] Caught exception socket.error: {exc}")
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finally:
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print("[*] Closing connection")
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try:
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client.close()
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except:
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pass
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def main():
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if len(sys.argv[1:]) == 0:
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print("Custom Netcat")
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print("\nSYNOPSIS")
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print(" netcat.py [OPTIONS...]\n")
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print("OPTIONS")
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print(" -l, --listen Start server in listening mode on specified host:port")
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print(" -e, --execute=<file> Execute specified file upon connection establishment")
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print(" -c, --command Initialize an interactive command shell session")
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print(" -u, --upload=<path> Upload file to specified destination path on connection")
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print(" -t, --target=<host> Specify target hostname or IP address")
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print(" -p, --port=<port> Specify target port number")
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print()
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sys.exit(0)
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try:
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opts, args = getopt.getopt(sys.argv[1:], "hle:t:p:cu:",
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["help", "listen", "execute", "target",
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"port", "command", "upload"])
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for o, a in opts:
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if o in ("-h", "--help"):
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main()
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elif o in ("-l", "--listen"):
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toolkit.listen = True
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elif o in ("-e", "--execute"):
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toolkit.execute = a
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elif o in ("-c", "--command"):
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toolkit.command = True
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elif o in ("-u", "--upload"):
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toolkit.upload_destination = a
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elif o in ("-t", "--target"):
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toolkit.target = a
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elif o in ("-p", "--port"):
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toolkit.port = int(a)
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else:
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assert False, "Unhandled Option"
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except getopt.GetoptError as err:
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print(str(err))
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main()
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signal.signal(signal.SIGINT, toolkit.signal_handler)
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signal.signal(signal.SIGTERM, toolkit.signal_handler)
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try:
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if not toolkit.listen and len(toolkit.target) and toolkit.port > 0:
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buffer = sys.stdin.read()
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toolkit.client_sender(buffer)
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if toolkit.listen:
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toolkit.server_loop()
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except KeyboardInterrupt:
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print("\n[*] User requested shutdown")
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except Exception as e:
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print(f"\n[!] Unexpected error: {str(e)}")
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finally:
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toolkit.running = False
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print("[*] Shutdown complete")
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sys.exit(0)
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if __name__ == "__main__":
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toolkit = NetCat("", 0)
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main()

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