It can open TCP connections, send UDP packets, listen on arbitrary TCP and UDP ports, do port scanning, and deal with both IPv4 and IPv6.Īnd it can do the same thing with: # nc -z “server ip” 1000 2000 3000 Pros and ConsĮverything has its advantages and disadvantages and port-knocking is not an exception to this rule: The nc (or netcat) utility is used for just about anything under the sun involving TCP, UDP, or UNIX domain sockets. # for x in 7000 8000 9000 do nmap -Pn –host_timeout 201 –max-retries 0 -p $x “server ip” done The Nmap is a Network exploration tool and security / port scanner, but you issue this command to initiate port-knocking: There are other ways to do Port-Knocking: Replace “server ip” with your server’s IP. On your client, issue this command: # knock “server ip” 7000 8000 9000 On your serverm issue the following command to run the port-knocking server: # knockd Port-Knocking Flags can be explicitly excluded by a “!” (e.g., TCPFlags = syn,!ack ). Separate multiple flags with commas (e.g., TCPFlags = syn, ack, urg). Using “TCPFlags = syn” is useful if you are testing over an SSH connection, as the SSH traffic will usually interfere with (and thus invalidate) the knock. This is different from the normal behavior, where an incorrect packet would invalidate the entire knock, forcing the client to start over. When using TCP flags, knockd will IGNORE TCP packets that don’t match the flags. That used sequence will then be replaced by the next valid sequence from the file.Īlso, TCPFlags directive can be these values: TCPFlags = fin|syn|rst|psh|ack|urg After each successful knock attempt, this sequence will be disabled by writing a ‘#’ character at the first position of the line containing the used sequence. Instead of using a fixed sequence, knockd will read the sequence to be used from that file. The above referenced file contains the one-time sequences to be used. One_Time_Sequences = /path/to/one_time_sequences_file One of the most important directives is One_Time_Sequences. The second command deletes the previous rule. The first command adds a rule number 00100 to ipfw that allows connection to SSH port by IP address of who knocked successfully.
The other two sections are for executing the command by a custom sequence of ports within five seconds that has a syn flag. An options section which is dedicated to interface name and log file. To facilitate that, we must first create a conf file from a sample and then add configurations: # cp /usr/local/etc/ /usr/local/etc/nfĬommand = /sbin/ipfw -q add 00100 pass proto tcp src-ip %IP% dst-port 22Ĭommand = /sbin/ipfw -q delete 00100 pass proto tcp src-ip %IP% dst-port 22Īs you can see, there are three sections and many directives. To configure knockd service, you have to edit nf. Tip: issue the above commands on both the client and the server.
#Brute force port knocking install
You can easily install it by port tree or pkg: # cd /usr/ports/security/knock There is a flexible Port-knocking server and client. In fact, Port-knocking has been used in many hacking tools, like rootkits.
#Brute force port knocking driver
Kernel-Module – Kernel-Module or device driver is more complicated, but it’s more stable.Daemon – With a simple daemon (service), you can run your port-knocked server.Port-knocking can be implemented in a number of ways, such as: The complexity of the knock can be anything from a simple ordered list (e.g., TCP port 1000, TCP port 2000, UDP port 3000) to a complex time-dependent, source-IP-based and other-factor-based encrypted hash. This can be used to open up holes in a firewall for quick access. When the server detects a specific sequence of port-hits, it runs a command defined in its configuration file. This port need not be open since knockd listens at the link-layer level, it sees all traffic even if it’s destined for a closed port. A client makes these port-hits by sending a TCP (or UDP) packet to a port on the server. A Port-knocking server listens to all traffic on an Ethernet (or PPP) interface, looking for special “knock” sequences of port-hits. Port-Knocking mitigates this type of security issues. Nmap will take care of this process, and it’s over. Hackers are going to find out what you are hiding by just a simple port scanner which takes about 2 minutes, nothing more. Changing the port numbers and services is a common mistake. Changing the port numbers is not a proper security policy.