Netcat
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netcat (often abbreviated to nc) is a computer networking utility for reading from and writing to network connections using TCP or UDP. The command is designed to be a dependable back-end that can be used directly or easily driven by other programs and scripts. 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.
It is able to perform port scanning, file transferring and port listening.
Features
The original netcat's features include:<ref>Template:Cite book</ref>
- Outbound or inbound connections, TCP or UDP, to or from any ports
- Full DNS forward/reverse 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
Rewrites like GNU's and OpenBSD's support additional features. For example, OpenBSD's nc supports TLS, and GNU netcat natively supports a tunneling mode supporting UDP and TCP (optionally allowing one to be tunneled over the other) in a single command,<ref>Template:Cite web</ref> where other versions may require piping data from one netcat instance to another.
Ports and reimplementations
The original version of netcat was a Unix program. The last version (1.10) was released in March 1996.<ref name="nc110">Template:Cite web</ref>
There are several implementations on POSIX systems, including rewrites from scratch like GNU netcat<ref>Template:Cite web</ref> or OpenBSD netcat,<ref>Template:Cite web</ref> the latter of which supports IPv6 and TLS. The OpenBSD version has been ported to the FreeBSD base,<ref>Template:Cite web</ref> Windows/Cygwin,<ref>Template:Cite web</ref> and Linux.<ref>Debian netcat-openbsd</ref> Mac OS X comes with netcat installed as of OSX 10.13 or users can use MacPorts to install a variant.<ref>Template:Cite web</ref>
A DOS version of netcat called NTOOL is included in the FreeDOS Package group Networking.<ref>Template:Cite web</ref> It is based on the WatTCP stack and licensed under the European Union Public Licence Version 1.1.<ref>Template:Cite web</ref>
Known ports for embedded systems includes versions for Windows CE (named "Netcat 4 wince"<ref>Template:Cite web</ref>) or for the iPhone.<ref>Template:Cite web</ref>
BusyBox includes by default a lightweight version of netcat named mini-netcat.<ref>Template:Cite web</ref> Another version with more features, named bloaty nc, is also available.<ref>Template:Cite web</ref>
Solaris 11 includes netcat implementation based on OpenBSD netcat.<ref>Template:Cite web</ref>
Socat<ref>Template:Cite web</ref> is a more complex variant of netcat. It is larger and more flexible and has more options that must be configured for a given task. On February 1, 2016, Santiago Zanella-Beguelin and Microsoft Vulnerability Research issued a security advisory regarding a composite Diffie-Hellman parameter which had been hard-coded into the OpenSSL implementation of socat.<ref name="socat-secadv7">Template:Cite web</ref> 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 backdoor software vulnerability.<ref>Template:Cite web</ref> This socat bug affected version 1.7.3.0 and 2.0.0-b8 it was corrected in following releases from 1.7.3.1 and 2.0.0-b9.<ref name="socat-secadv7"/>
Cryptcat<ref>Template:Cite web</ref> is a version of netcat with integrated transport encryption capabilities.
In the middle of 2005, Nmap announced another netcat incarnation called Ncat.<ref name="ncat">Template:Cite web</ref> It features new possibilities such as "Connection Brokering", TCP/UDP Redirection, SOCKS4 client and server support, ability to "Chain" Ncat processes, HTTP CONNECT proxying (and proxy chaining), SSL connect/listen support and IP address/connection filtering. Like Nmap, Ncat is cross-platform.
On some systems, modified versions or similar netcat utilities go by the command name(s) nc, ncat, pnetcat, socat, sock, socket, sbd.
ncat
Ncat is a similar tool to netcat provided by Nmap suite.<ref name="ncat"/> "While Ncat isn't built on any code from the “traditional” Netcat (or any other implementation), Ncat is most definitely based on Netcat in spirit and functionality."<ref>Template:Cite web</ref>
Ncat features includes: ability to chain Ncats together, redirect both TCP and UDP ports to other sites, SSL support, and proxy connections via SOCKS4 or HTTP (CONNECT method) proxies (with optional proxy authentication as well).<ref>Template:Cite web</ref>