Netcat Wikipedia. Netcat often abbreviated to nc is a computer networking utility for reading from and writing to network connections using TCP or UDP. Netcat is designed to be a dependable back end that can be used directly or easily driven by other programs and scripts. Bored Heres 101 Useful Websites With Easy to Remember Names Updated Fix Most Windows Errors and Problems With Tweaking. Com Windows Repair 4. Video. This is a list of the most common TCP and UDP port numbers. Port numbers range from 0 to 65536, but only ports numbers 0 to 1024 are designated as wellknown ports. Experts Exchange Questions ORA12505 TNSlistener could not resolve SID given in connect descriptor. How to prepare a Windows VHD or VHDX before uploading to Azure. Some quick notes on what nmap scans by default, the commands below will give you the ranges scanned, and theres also some lists suitable for copypasting. Top 1,000. At the same time, it is a feature rich network debugging and investigation tool, since it can produce almost any kind of connection its user could need and has a number of built in capabilities. Its list of features includes port scanning, transferring files, and port listening, and it can be used as a backdoor. FeatureseditThe original netcats features include 1Outbound or inbound connections, TCP or UDP, to or from any ports. SS4.jpg?revision=1&size=bestfit&width=782&height=573' alt='Tcp Listener Tool Windows 7' title='Tcp Listener Tool Windows 7' />Full DNS forwardreverse checking, with appropriate warnings. Ability to use any local source port. Ability to use any locally configured network source address. Built in port scanning capabilities, with randomization. Built in loose source routing capability. Can read command line arguments from standard input. Slow send mode, one line every N seconds. Hex dump of transmitted and received data. Optional ability to let another program service establish connections. Optional telnet options responder. Featured tunneling mode which permits user defined tunneling, e. UDP or TCP, with the possibility of specifying all network parameters source portinterface, listening portinterface, and the remote host allowed to connect to the tunnel. Rewrites like GNUs and Open. BSDs support additional features. For example, Open. BSDs nc supports TLS. ExampleseditOpening a raw connection to port 2. SMTPedit. nc mail. Setting up a one shot webserver on port 8. HTTP1. 0 2. 00 OKrn. Content Length drnrnwc c lt some. The file can then be accessed via a web browser under http servername 8. Netcat only serves the file once to the first client that connects and then exits it also provides the content length for browsers that expect it. This should work fine in a LAN, but may potentially fail with any kind of firewall between. In some versions of netcat like netcat traditional in Debian 8. Checking whether UDP ports u 8. IO zedit. nc vzu 1. Note that UDP tests will always show as open. The z argument is useless. Test whether UDP port is open simple UDP server and clienteditThis test is useful, if you have shell access to the server that should be tested, but you do not know whether there is a firewall blocking a specific UDP port on the server. On the listening host, i. On the sending host, do the following note that servname is the hostname of the listening host. If text typed on the sending host type something and hit enter is displayed also on the listening host, then the UDP port 7. If it is not open, you will get an error such as Connection refused. There is a caveat. Sdr Radio Software here. On some machines, IPv. IP version to use by netcat. Thus, the host specified by the hostname is contacted using IPv. Ports may appear closed in the test, even though they would be open when using IPv. This can be difficult to notice and may cause the false impression that the port is blocked, while it is actually open. You can force the use of IPv. Pipe via UDP u with a wait time w of 1 second to loggerhost on port 5. Port scanningeditAn uncommon use of netcat is port scanning. Netcat is not considered the best tool for this job, but it can be sufficient a more advanced tool is nmap. The n parameter here prevents DNS lookup, z makes nc not receive any data from the server, and w 1 makes the connection timeout after 1 second of inactivity. ProxyingeditAnother useful behaviour is using netcat as a proxy. Both ports and hosts can be redirected. Look at this example. Port 1. 23. 45 represents the request. This starts a nc server on port 1. If a web browser makes a request to nc, the request will be sent to google but the response will not be sent to the web browser. That is because pipes are unidirectional. This can be worked around with a named pipe to redirect the input and output. The c option may also be used with the ncat implementation 2. Using a named pipe is a more reliable method because using c option provides only a one shot proxy. Another useful feature is to proxy SSL connections. This way, the traffic can not be viewed in wire sniffing applications such as wireshark. This can be accomplished on UNIXes by utilizing mkfifo, netcat, and openssl. Making any process a servereditnetcat can be used to make any process a network server. It can listen on a port and pipe the input it receives to that process. The e option spawns the executable with its input and output redirected via network socket. For example, it is possible to expose a bourne shell process to remote computers. To do so, on a computer A with IP address 1. Then, from any other computer on the same network, one could run this nc command nc 1. In this way, the e option can be used to create a rudimentary backdoor. Some administrators perceive this as a risk and thus do not allow netcat on a computer. Examples by netcat Debian 8. Connect to example. TCP port 8. 08. 0. Listen for connections on TCP port 8. Lian 98. Redirect TCP port 8. Bind to TCP port 8. Bind a shell to TCP port 8. Connect to smtphost 2. SOCKS4 server on port 1. Create an HTTP proxy server on localhost port 8. Send a file over TCP port 9. HOST1 ncat l 9. HOST2 ncat HOST1 9. Transfer in the other direction, turning Ncat into a one file server. HOST1 ncat l 9. HOST2 ncat HOST1 9. Encrypted file transfer3editSuppose you have an SSH tunnel, and you want to copy a file to the remote machine. You could just scp it directly, but that opens up another connection. The goal is to re use the existing connection. You can use netcat to do this When you SSH in, add L 3. On the remote nc lvnp 3. On the local nc v w 2 1. No extra overhead. TCP takes care of error correction. SSH has already encrypted the pipe. Ports and reimplementationseditThe original version of netcat was a Unix program. The last version 1. March 1. 99. 6. 1There are several implementations on POSIX systems, including rewrites from scratch like GNU netcat4 or Open. BSD netcat,5 the latter of which supports IPv. TLS. The Open. BSD version has been ported to the Free. BSD base6 and WindowsCygwin. Mac OS X users can use Mac. Ports to install a netcat variant. There is also a Microsoft Windows version of netcat available. Known ports for embedded systems includes versions for Windows CE named Netcat 4 wince1. Phone. 1. 1Busy. Box includes by default a lightweight version of netcat. Solaris 1. 1 includes netcat implementation based on Open. BSD netcat. Socat1. It is larger and more flexible and has more options that must be configured for a given task. On February 1, 2. Santiago Zanella Beguelin and Microsoft Vulnerability Research issued a security advisory regarding a composite. Diffie Hellman parameter which had been hard coded into the Open. SSL implementation of socat. The implausibility that a composite might have been unintentionally introduced where a prime number is required has led to the suspicion of sabotage to introduce a backdoorsoftware vulnerability. Cryptcat1. 3 is a version of netcat with integrated transport encryption capabilities. In the middle of 2. Nmap announced another netcat incarnation called Ncat.