How does an Xmas scan work?
An adversary uses a TCP XMAS scan to determine if ports are closed on the target machine. This scan type is accomplished by sending TCP segments with all possible flags set in the packet header, generating packets that are illegal based on RFC 793.
What is the purpose of Xmas scan in Nmap?
Xmas scan ( -sX ) Sets the FIN, PSH, and URG flags, lighting the packet up like a Christmas tree. These three scan types are exactly the same in behavior except for the TCP flags set in probe packets.
Which of the following flags will trigger Xmas scan?
Explanation. From nmap.org: "Xmas scan (-sX) Sets the FIN, PSH, and URG flags, lighting the packet up like a Christmas tree."
What is the proper command to perform an Nmap Xmas scan?
nmap -sX commandNmap Xmas Scan can be performed using nmap -sX command.
Is it legal to scan with Nmap?
Network probing or port scanning tools are only permitted when used in conjunction with a residential home network, or if explicitly authorized by the destination host and/or network. Unauthorized port scanning, for any reason, is strictly prohibited.
Is Nmap scanning safe?
Nmap is a safe tool, and it's also a dependable software that's available for cybersecurity professionals. However, it's understandable that nothing is really safe. Even Windows and builds of Linux contact vulnerabilities. There may be some restricted environment where it's against the rules to install it.
How do I know if someone is port scanning me?
Normally, port scans trigger huge amounts of requests to different ports or IP Addresses within a short period of time. Such port scans can be easily detected by simple mechanisms like counting the number of requested ports for each Source IP Address.
How do you know that a port being scanned is open?
When you send a port scan with a packet and the FIN flag, you send the packet and not expecting a response. If you do get an RST, you can assume that the port is closed. If you get nothing back, that indicates the port is open.
What is the response of an Xmas scan if a port is either open or filtered?
Open|filtered: Nmap can't detect if the port is open or filtered. Even if the port is open, the Xmas scan will report it as open|filtered. It happens when no response is received (even after retransmissions). Closed: Nmap detects the port is closed; it happens when the response is a TCP RST packet.
What are the three types of scanning?
Scanning is primarily of three types. These are network scanning, port scanning, and vulnerability scanning.
What is vanilla scanning?
A vanilla scan is a full connect scan, meaning it sends a SYN flag (request to connect) and upon receiving a SYN-ACK (acknowledgement of connection) response, sends back an ACK flag. This SYN, SYN-ACK, ACK exchange comprises a TCP handshake.
How long does a Nmap scan take?
Estimate and Plan for Scan Time So the total time Nmap will spend scanning the network can be roughly extrapolated by multiplying 21 minutes per host by the number of hosts online. If version detection or UDP are being done as well, you'll also have to watch the timing estimates for those.
What are Xmas packets?
Christmas tree packets can be used as a method of TCP/IP stack fingerprinting, exposing the underlying nature of a TCP/IP stack by sending the packets and then awaiting and analyzing the responses. When used as part of scanning a system, the TCP header of a Christmas tree packet has the flags FIN, URG and PSH set.
Which scan type will produce the same response as an Xmas scan?
XMAS scans work only on target systems that follow the RFC 793 implementation of TCP/IP and don't work against any version of Windows. FIN - A FIN scan is similar to an XMAS scan but sends a packet with just the FIN flag set. FIN scans receive the same response and have the same limitations as XMAS scans.
What is the purpose of host scanning?
This activity, called host discovery, starts by doing a network scan. The goal behind port and network scanning is to identify the organization of IP addresses, hosts, and ports to properly determine open or vulnerable server locations and diagnose security levels.
What will an open port return from an ACK scan using Nmap?
The ACK scan probe packet has only the ACK flag set (unless you use --scanflags ). When scanning unfiltered systems, open and closed ports will both return a RST packet. Nmap then labels them as unfiltered , meaning that they are reachable by the ACK packet, but whether they are open or closed is undetermined.
How do Xmas scans work?
Xmas scans derive their name from the set of flags that are turned on within a packet. These scans are designed to manipulate the PSH, URG and FIN flag s of the TCP header. When viewed within Wireshark, we can see that alternating bits are enabled, or “Blinking,” much like you would light up a Christmas tree. This is the humor we techies love.
Why do we do Xmas scans?
So in other words, the Xmas scan in order to identify listening ports on a targeted system will send a specific packet. If the port is open on the target system then the packets will be ignored. If closed then an RST will be sent back to the individual running the scan. Xmas scans were popular not only because of their speed compared to other scans but because of there similarity to out of state FIN and ACK packets that could easily bypass stateless firewalls and ACL filters. They do however run into problems with various operating systems that do not conform to RFC 793. These systems will send a RST response when any malformed TCP segment is received by a listening socket instead of dropping it. The attackers are then left guessing to which ports are open and which are closed.
Does NetFlow scan have holiday spirit?
This scan actually lacks any actual holiday spirit and should be investigated. As we dig deeper into the alarms from our NetFlow collector, we can see the violator, the victim, the exporter that saw the scan and time frame. This will give us enough information to begin our investigation to find the root cause.
What is a nmap Xmas scan?
Nmap Xmas scan was considered a stealthy scan which analyzes responses to Xmas packets to determine the nature of the replying device. Each operating system or network device responds in a different way to Xmas packets revealing local information such as OS (Operating System), port state and more. Currently many firewalls and Intrusion Detection System can detect Xmas packets and it is not the best technique to carry out a stealth scan, yet it is extremely useful to understand how it works.
Is Xmas a filtered port?
The Xmas scan, just as the NULL and FIN scan can’ t distinguish between a closed and filtered port, as mentioned above, is the packet response is an ICMP error Nmap tags it as filtered, but as explained on Nmap book if the probe is banned without response it seems opened, therefore Nmap shows open ports and certain filtered ports as open|filtered
Is the Xmas scan new?
While the Xmas scan isn’t new and most defense systems are capable to detect it becoming an obsolete technique against well protected targets it is a great way of introduction to uncommon TCP segments like PSH and URG and to understand the way in which Nmap analyzes packets get conclusions on targets. More than an attack method this scan is useful ...
What is a Christmas tree attack?
A Christmas Tree Attack is a very well known attack that is designed to send a very specifically crafted TCP packet to a device on the network. This crafting of the packet is one that turns on a bunch of flags. There is some space set up in the TCP header, called flags. And these flags all are turned on or turned off, depending on what the packet is doing.
Does a Christmas tree scan bring down my router?
So now I can be assured that a Christmas tree scan is not going to bring down my brand new router. That’s something you need to keep in mind. If somebody is performing these scans on your network and they’re causing systems to go offline or causing a denial of service situation, then you may need to get updated firmware. You may need to get updated hardware. Or find out what you can do to prevent somebody in your network from causing a denial of service to your very, very important systems.
How to detect Christmas tree packets?
Christmas tree packets can be easily detected by intrusion-detection systems or more advanced firewalls. From a network security point of view, Christmas tree packets are always suspicious and indicate a high probability of network reconnaissance activities.
How does a Christmas tree packet work?
Christmas tree packets can be used as a method of TCP/IP stack fingerprinting, exposing the underlying nature of a TCP/IP stack by sending the packets and then awaiting and analyzing the responses . When used as part of scanning a system, the TCP header of a Christmas tree packet has the flags FIN, URG and PSH set. Many operating systems implement their compliance with the Internet Protocol standards in varying or incomplete ways. By observing how a host responds to an odd packet, such as a Christmas tree packet, inferences can be made regarding the host's operating system. Versions of Microsoft Windows, BSD/OS, HP-UX, Cisco IOS, MVS, and IRIX display behaviors that differ from the RFC standard when queried with said packets.
Can a Christmas tree be used for a DoS attack?
A large number of Christmas tree packets can also be used to conduct a DoS attack by exploiting the fact that Christmas tree packets require much more processing by routers and end-hosts than the "usual" packets do.
