Linux Tactic

Unwrapping the Xmas Scan: Testing Your Network Security With a Stealthy Technique

Nmap Xmas Stealth Scan Technique: Understanding the Vulnerabilities of Your Firewall and Intrusion Detection Systems

Are you sure that your firewall and Intrusion Detection System (IDS) are secure? Do you know that there is an ancient method that can help you test the effectiveness of your network security?

The method is called the Xmas Scan technique, which is why it is essential to know the ins and outs of this stealthy scan method.

Understanding Xmas Scan

The Xmas Scan is a stealthy scan method that is used to identify open and closed ports and is less detectable by IDS and firewalls. This scan technique is named Xmas because it resembles the blinking Christmas lights that come on and off.

This method is called a stealthy scan because it sends a packet with Christmas tree like TCP flags to the targeted host, which expects a certain pattern of incoming and outgoing packets to allow traffic. When this pattern is disrupted, it becomes possible to identify open and closed ports.

Xmas Scan Port States

Executing an Xmas scan using the Nmap tool is simple and can provide you with valuable information on your network security. The following states can be expected upon execution:

– Open|Filtered: There is a possibility of an open port of the host but can also be a result of stateful firewall implementation.

– Closed: There is no service running on the scanned port. – Filtered: The port is unreachable, and there’s a firewall protection mechanism that resulted in port masking.

Executing Xmas Scan with Nmap

Executing an Xmas scan with Nmap, you can use the following syntax:

nmap sX target_ip_address

Also, you can use the timing template flags from T0 (Paranoid) to T5 (Insane) to change the aggressivity level of your scan. However, too much aggressive scanning can lead to IPS (Intrusion Prevention System) or IDS false positives.

Other Similar Scans – NULL and FIN Scans

Other scans can be used to identify vulnerabilities in firewalls, such as the NULL scan and FIN scan. The NULL scan is slightly different from the Xmas scan in that it only sends packets with no flags to the host.

This method comes in handy when dealing with stateless firewalls. The FIN scan involves sending a packet with the FIN flag set to the target host’s port.

This method is effective in detecting open ports on a host when the attacker can interrupt the communication between the two.

SYN Stealth Scan

The SYNScan works differently than the Xmas scan, but it is just as effective. The difference lies in the packet sent, which is a SYN packet rather than a combination of different flags.

This method is less aggressive than Xmas Scans and is less likely to be picked up by IDS. However, it is still detectable and can be logged by the server’s operating system, making it an excellent alternative to Xmas Scans.

Understanding FIN, PSH, and URG Bits

When using the Xmas scan method, it’s important to understand the TCP protocol and the meaning of the flags you are sending to the host. The PSH (Push), URG (Urgent) and FIN (Finish) bits indicate the type of interaction between the attacker and the host.

The PUSH bit pushes data to TCP buffers for quicker transmission, while the URG is used to send urgent data that is of higher priority. Meanwhile, the FIN bit closes the connection between the host and the attacker.

Iptables Rules Against Xmas Scans

Iptables rules can be implemented to prevent Xmas scans from occurring. These rules allow for packet filtering and can be set up automatically by most firewall solutions.

Enabling IP communication from trusted sources is an ideal firewall setting to mitigate the impact of Xmas Scans.

Understanding the Educational Value of Xmas Scan

Xmas Scan serves as one of the earliest lessons on TCP structure. It also helps in testing the effectiveness of your network security and gives you an idea of vulnerabilities that may exist.

Finally, by running an Xmas scan, you can detect and gain insight into the limitations of your firewall and IDS, giving you the presence of mind to make improvements.


Xmas Scan is a useful and undetectable tool for testing network security, and you should implement it to assess your firewall and IDS’s effectiveness. Also, employing other methods such as the FIN and NULL scans can uncover vulnerabilities that the Xmas scan may not.

With the correct implementation of Iptables rules and a solid understanding of TCP protocol and its flags, you can create a robust network that is immune to attacks. In summary, the Nmap Xmas Stealth Scan Technique is an ancient but effective method for testing the security of your firewall and Intrusion Detection System.

Understanding how to execute an Xmas scan, its benefits, and other similar scan methods like NULL, FIN, and SYN stealth scans, and the Iptables rules that can be employed against Xmas scans are essential skills for maintaining a secure network. By analyzing the vulnerabilities of your network system, you can identify any potential risks and improve your security measures to prevent cyber attacks.

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