Windows客户端防火墙开启时端口扫描失败的相关技术咨询

Question 1: Method to Get Responses Regardless of Firewall State #

If you're performing local port scanning (scanning the same Windows machine your code runs on), you can completely bypass firewall restrictions by querying the OS's internal network state instead of sending external network packets. This works because you're accessing the system's own network stack data directly, which isn't filtered by the firewall.

Practical Implementation (Python) #

Use libraries like psutil (a cross-platform tool that wraps Windows API functions like GetTcpTable2) to retrieve active listeners and connections:

import psutil

def get_local_open_ports():
    open_ports = []
    # Fetch TCP listening ports
    for conn in psutil.net_connections(kind='tcp'):
        if conn.status == psutil.CONN_LISTEN:
            open_ports.append(conn.laddr.port)
    # Fetch UDP bound ports (UDP is connectionless, so check active binds)
    for sock in psutil.net_sockets(kind='udp'):
        if sock.family == 2:  # Target IPv4 addresses
            open_ports.append(sock.laddr.port)
    return list(set(open_ports))  # Remove duplicates

print("Local open ports:", get_local_open_ports())

For remote port scanning, there’s no guaranteed way to bypass an active firewall unless the target port is explicitly allowed. However, you can try:

• ICMP Echo Requests (Ping): Many firewalls allow ICMP by default, so this can confirm the remote host is up even if ports are blocked.
• TCP SYN Scans: These "half-open" scans are less likely to trigger logs, but modern firewalls still detect and block them. Note that raw socket access for SYN scans requires admin privileges on Windows and is restricted by default.

Question 2: Always Open Ports in Windows #

Windows does not have a universal, always-open port that works across all versions, editions, and configurations. System services that open default ports (like DNS on 53 or DHCP on 67/68) can be disabled, and firewalls can block even these default ports.

Local Workaround #

If you need a reliable way to get a response locally, you can create your own listening socket on the loopback interface (127.0.0.1). Local loopback traffic is almost always exempt from firewall rules, even when the firewall is enabled:

import socket
import threading

def local_listener(port):
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.bind(('127.0.0.1', port))
    s.listen(1)
    conn, _ = s.accept()
    conn.close()
    s.close()

# Start a listener in a background thread
target_port = 8080
threading.Thread(target=local_listener, args=(target_port,), daemon=True).start()

# Connect to the local listener
client_sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
try:
    client_sock.connect(('127.0.0.1', target_port))
    print(f"Successfully connected to local port {target_port} (firewall bypassed)")
except Exception as e:
    print(f"Connection failed: {str(e)}")
client_sock.close()

For remote hosts, your best bet is to check common ports that are often open (like 80, 443 for web services), but there’s no guarantee they’ll be accessible through a firewall.

内容的提问来源于stack exchange，提问作者Pr Mod