# ncat

## NAME



           ncat - Concatenate and redirect sockets
    


## SYNOPSIS



    
           **ncat**[_OPTIONS_...] [_hostname_] [_port_]
    


## DESCRIPTION



           Ncat is a feature-packed networking utility which reads and writes
           data across networks from the command line. Ncat was written for
           the Nmap Project and is the culmination of the currently
           splintered family of Netcat incarnations. It is designed to be a
           reliable back-end tool to instantly provide network connectivity
           to other applications and users. Ncat will not only work with IPv4
           and IPv6 but provides the user with a virtually limitless number
           of potential uses.
    
           Among Ncat's vast number of features there is the ability to chain
           Ncats together; redirection of TCP, UDP, and SCTP ports to other
           sites; SSL support; and proxy connections via SOCKS4, SOCKS5 or
           HTTP proxies (with optional proxy authentication as well). Some
           general principles apply to most applications and thus give you
           the capability of instantly adding networking support to software
           that would normally never support it.
    


## OPTIONS SUMMARY



               Ncat 7.98SVN ( https://nmap.org/ncat )
               Usage: ncat [options] [hostname] [port]
    
               Options taking a time assume seconds. Append 'ms' for milliseconds,
               's' for seconds, 'm' for minutes, or 'h' for hours (e.g. 500ms).
                 -4                         Use IPv4 only
                 -6                         Use IPv6 only
                 -U, --unixsock             Use Unix domain sockets only
                     --vsock                Use vsock sockets only
                 -C, --crlf                 Use CRLF for EOL sequence
                 -c, --sh-exec <command>    Executes the given command via /bin/sh
                 -e, --exec <command>       Executes the given command
                     --lua-exec <filename>  Executes the given Lua script
                 -g hop1[,hop2,...]         Loose source routing hop points (8 max)
                 -G <n>                     Loose source routing hop pointer (4, 8, 12, ...)
                 -m, --max-conns <n>        Maximum <n> simultaneous connections
                 -h, --help                 Display this help screen
                 -d, --delay <time>         Wait between read/writes
                 -o, --output <filename>    Dump session data to a file
                 -x, --hex-dump <filename>  Dump session data as hex to a file
                 -i, --idle-timeout <time>  Idle read/write timeout
                 -p, --source-port port     Specify source port to use
                 -s, --source addr          Specify source address to use (doesn't affect -l)
                 -l, --listen               Bind and listen for incoming connections
                 -k, --keep-open            Accept multiple connections in listen mode
                 -n, --nodns                Do not resolve hostnames via DNS
                 -t, --telnet               Answer Telnet negotiations
                 -u, --udp                  Use UDP instead of default TCP
                     --sctp                 Use SCTP instead of default TCP
                 -v, --verbose              Set verbosity level (can be used several times)
                 -w, --wait <time>          Connect timeout
                 -z                         Zero-I/O mode, report connection status only
                     --append-output        Append rather than clobber specified output files
                     --send-only            Only send data, ignoring received; quit on EOF
                     --recv-only            Only receive data, never send anything
                     --no-shutdown          Continue half-duplex when receiving EOF on stdin
                 -q <time>                  After EOF on stdin, wait <time> then quit.
                     --allow                Allow only given hosts to connect to Ncat
                     --allowfile            A file of hosts allowed to connect to Ncat
                     --deny                 Deny given hosts from connecting to Ncat
                     --denyfile             A file of hosts denied from connecting to Ncat
                     --broker               Enable Ncat's connection brokering mode
                     --chat                 Start a simple Ncat chat server
                     --proxy <addr[:port]>  Specify address of host to proxy through
                     --proxy-type <type>    Specify proxy type ("http", "socks4", "socks5")
                     --proxy-auth <auth>    Authenticate with HTTP or SOCKS proxy server
                     --proxy-dns <type>     Specify where to resolve proxy destination
                     --ssl                  Connect or listen with SSL
                     --ssl-cert             Specify SSL certificate file (PEM) for listening
                     --ssl-key              Specify SSL private key (PEM) for listening
                     --ssl-verify           Verify trust and domain name of certificates
                     --ssl-trustfile        PEM file containing trusted SSL certificates
                     --ssl-ciphers          Cipherlist containing SSL ciphers to use
                     --ssl-servername       Request distinct server name (SNI)
                     --ssl-alpn             ALPN protocol list to use
                     --version              Display Ncat's version information and exit
    
               See the ncat(1) manpage for full options, descriptions and usage examples
    


## CONNECT MODE AND LISTEN MODE



           Ncat operates in one of two primary modes: connect mode and listen
           mode. Other modes, such as the HTTP proxy server, act as special
           cases of these two. In connect mode, Ncat works as a client. In
           listen mode it is a server.
    
           In connect mode, the _hostname_ and _port_ arguments tell what to
           connect to.  _hostname_ is required, and may be a hostname or IP
           address. If _port_ is supplied, it must be a decimal port number. If
           omitted, it defaults to 31337.
    
           In listen mode, _hostname_ and _port_ control the address the server
           will bind to. Both arguments are optional in listen mode. If
           _hostname_ is omitted, it defaults to listening on all available
           addresses over IPv4 and IPv6. If _port_ is omitted, it defaults to
           31337.
    


## PROTOCOL OPTIONS



           **-4**(IPv4 only)
               Force the use of IPv4 only.
    
           **-6**(IPv6 only)
               Force the use of IPv6 only.
    
           **-U** , **--unixsock**(Use Unix domain sockets)
               Use Unix domain sockets rather than network sockets. This
               option may be used on its own for stream sockets, or combined
               with **--udp** for datagram sockets. A description of **-U** mode is
               in the section called “UNIX DOMAIN SOCKETS”.
    
           **-u** , **--udp**(Use UDP)
               Use UDP for the connection (the default is TCP).
    
           **--sctp**(Use SCTP)
               Use SCTP for the connection (the default is TCP). SCTP support
               is implemented in TCP-compatible mode.
    
           **--vsock**(Use AF_VSOCK sockets)
               Use AF_VSOCK sockets rather than the default TCP sockets
               (Linux only). This option may be used on its own for stream
               sockets or combined with **--udp** for datagram sockets. A
               description of **--vsock** mode is in the section called “AF_VSOCK
               SOCKETS”.
    


## CONNECT MODE OPTIONS



           **-g** _hop1_**[,**_hop2_ ,...] (Loose source routing)
               Sets hops for IPv4 loose source routing. You can use **-g** once
               with a comma-separated list of hops, use **-g** multiple times
               with single hops to build the list, or combine the two. Hops
               can be given as IP addresses or hostnames.
    
           **-G** _ptr_ (Set source routing pointer)
               Sets the IPv4 source route “pointer” for use with **-g**. The
               argument must be a multiple of 4 and no more than 28. Not all
               operating systems support setting this pointer to anything
               other than four.
    
           **-p** _port_ , **--source-port** _port_ (Specify source port)
               Set the port number for Ncat to bind to.
    
           **-s** _host_ , **--source** _host_ (Specify source address)
               Set the address for Ncat to bind to.
    


## LISTEN MODE OPTIONS



           See the section called “ACCESS CONTROL OPTIONS” for information on
           limiting the hosts that may connect to the listening Ncat process.
    
           **-l** , **--listen**(Listen for connections)
               Listen for connections rather than connecting to a remote
               machine
    
           **-m** _numconns_ , **--max-conns** _numconns_ (Specify maximum number of
           connections)
               The maximum number of simultaneous connections accepted by an
               Ncat instance. 100 is the default (60 on Windows).
    
           **-k** , **--keep-open**(Accept multiple connections, do not quit on
           socket EOF)
               Normally a listening server accepts only one connection and
               then quits when the connection is closed. This option makes it
               accept multiple simultaneous connections and wait for more
               connections after they have all been closed. It must be
               combined with **--listen**. In this mode there is no way for Ncat
               to know when its network input is finished, so it will keep
               running until interrupted. This also means that it will never
               close its output stream, so any program reading from Ncat and
               looking for end-of-file will also hang.
    
               In connect mode, the **-k** option has a different meaning: when
               the remote end of a TCP connection shuts down its side of the
               connection, Ncat will keep running and sending any available
               data. This was the default behavior in Ncat 7.95 and earlier,
               but it was changed to better align with existing netcat
               implementations. TCP is the only transport that supports this
               option in connect mode.
    
           **--broker**(Connection brokering)
               Allow multiple parties to connect to a centralised Ncat server
               and communicate with each other. Ncat can broker communication
               between systems that are behind a NAT or otherwise unable to
               directly connect. This option is used in conjunction with
               **--listen** , which causes the **--listen** port to have broker mode
               enabled.
    
           **--chat**(Ad-hoc “chat server”)
               The **--chat** option enables chat mode, intended for the exchange
               of text between several users. In chat mode, connection
               brokering is turned on. Ncat prefixes each message received
               with an ID before relaying it to the other connections. The ID
               is unique for each connected client. This helps distinguish
               who sent what. Additionally, non-printing characters such as
               control characters are escaped to keep them from doing damage
               to a terminal.
    


## SSL OPTIONS



           **--ssl**(Use SSL)
               In connect mode, this option transparently negotiates an SSL
               session with an SSL server to securely encrypt the connection.
               This is particularly handy for talking to SSL enabled HTTP
               servers, etc.
    
               In server mode, this option listens for incoming SSL
               connections, rather than plain untunneled traffic.
    
               In UDP mode, this option enables Datagram TLS (DTLS).
    
           **--ssl-verify**(Verify server certificates)
               In client mode, **--ssl-verify** is like **--ssl** except that it also
               requires verification of the server certificate. Ncat comes
               with a default set of trusted certificates in the file
               ca-bundle.crt.  Some operating systems provide a default list
               of trusted certificates; these will also be used if available.
               Use **--ssl-trustfile** to give a custom list. Use **-v** one or more
               times to get details about verification failures.  Ncat does
               not check for revoked certificates.
    
               This option has no effect in server mode.
    
           **--ssl-cert** _certfile.pem_ (Specify SSL certificate)
               This option gives the location of a PEM-encoded certificate
               files used to authenticate the server (in listen mode) or the
               client (in connect mode). Use it in combination with
               **--ssl-key**.
    
           **--ssl-key** _keyfile.pem_ (Specify SSL private key)
               This option gives the location of the PEM-encoded private key
               file that goes with the certificate named with **--ssl-cert**.
    
           **--ssl-trustfile** _cert.pem_ (List trusted certificates)
               This option sets a list of certificates that are trusted for
               purposes of certificate verification. It has no effect unless
               combined with **--ssl-verify**. The argument to this option is the
               name of a PEM file containing trusted certificates. Typically,
               the file will contain certificates of certification
               authorities, though it may also contain server certificates
               directly. When this option is used, Ncat does not use its
               default certificates.
    
           **--ssl-ciphers** _cipherlist_ (Specify SSL ciphersuites)
               This option sets the list of ciphersuites that Ncat will use
               when connecting to servers or when accepting SSL connections
               from clients. The syntax is described in the OpenSSL
               ciphers(1) man page, and defaults to
               ALL:!aNULL:!eNULL:!LOW:!EXP:!RC4:!MD5:@STRENGTH
    
           **--ssl-servername** _name_ (Request distinct server name)
               In client mode, this option sets the TLS SNI (Server Name
               Indication) extension, which tells the server the name of the
               logical server Ncat is contacting. This is important when the
               target server hosts multiple virtual servers at a single
               underlying network address. If the option is not provided, the
               TLS SNI extension will be populated with the target server
               hostname.
    
           **--ssl-alpn** _ALPN list_ (Specify ALPN protocol list)
               This option allows you to specify a comma-separated list of
               protocols to send via the Application-Layer Protocol
               Negotiation (ALPN) TLS extension. Not supported by all
               versions of OpenSSL.
    


## PROXY OPTIONS



           **--proxy** _host_**[:**_port_] (Specify proxy address)
               Requests proxying through _host_ :_port_ , using the protocol
               specified by **--proxy-type**.
    
               If no port is specified, the proxy protocol's well-known port
               is used (1080 for SOCKS and 3128 for HTTP). When specifying an
               IPv6 HTTP proxy server using the IP address rather than the
               hostname, the square-bracket notation (for example
               [2001:db8::1]:8080) MUST be used to separate the port from the
               IPv6 address. If the proxy requires authentication, use
               **--proxy-auth**.
    
           **--proxy-type** _proto_ (Specify proxy protocol)
               In connect mode, this option requests the protocol _proto_ to
               connect through the proxy host specified by **--proxy**. In listen
               mode, this option has Ncat act as a proxy server using the
               specified protocol.
    
               The currently available protocols in connect mode are http
               (CONNECT), socks4 (SOCKSv4), and socks5 (SOCKSv5). The only
               server currently supported is http. If this option is not
               used, the default protocol is http.
    
           **--proxy-auth** _user_**[:**_pass_] (Specify proxy credentials)
               In connect mode, gives the credentials that will be used to
               connect to the proxy server. In listen mode, gives the
               credentials that will be required of connecting clients. For
               use with **--proxy-type http** or **--proxy-type socks5** , the form
               should be username:password. For **--proxy-type socks4** , it
               should be a username only.
    
               These credentials can be alternatively passed onto Ncat by
               setting environment variable **NCAT_PROXY_AUTH** , which reduces
               the risk of the credentials being captured in process logs.
               (Option **--proxy-auth** takes precedence.)
    
           **--proxy-dns** _type_ (Specify where to resolve proxy destination)
               In connect mode, it provides control over whether proxy
               destination hostnames are resolved by the remote proxy server
               or locally, by Ncat itself. Possible values for _type_ are:
    
               local - Hostnames are resolved locally on the Ncat host. Ncat
               exits with error if the hostname cannot be resolved.
    
               remote - Hostnames are passed directly onto the remote proxy
               server. This is the default behavior.
    
               both - Hostname resolution is first attempted on the Ncat
               host. Unresolvable hostnames are passed onto the remote proxy
               server.
    
               none - Hostname resolution is completely disabled. Only a
               literal IPv4 or IPv6 address can be used as the proxy
               destination.
    
               Local hostname resolution generally respects IP version
               specified with options **-4** or **-6** , except for SOCKS4, which is
               incompatible with IPv6.
    


## COMMAND EXECUTION OPTIONS



           **-e** _command_ , **--exec** _command_ (Execute command)
               Execute the specified command after a connection has been
               established. The command must be specified as a full pathname.
               All input from the remote client will be sent to the
               application and responses sent back to the remote client over
               the socket, thus making your command-line application
               interactive over a socket. Combined with **--keep-open** , Ncat
               will handle multiple simultaneous connections to your
               specified port/application like inetd. Ncat will only accept a
               maximum, definable, number of simultaneous connections
               controlled by the **-m** option. By default this is set to 100 (60
               on Windows).
    
           **-c** _command_ , **--sh-exec** _command_ (Execute command via sh)
               Same as **-e** , except it tries to execute the command via
               /bin/sh. This means you don't have to specify the full path
               for the command, and shell facilities like environment
               variables are available.
    
           **--lua-exec** _file_ (Execute a .lua script)
               Runs the specified file as a Lua script after a connection has
               been established, using a built-in interpreter. Both the
               script's standard input and the standard output are redirected
               to the connection data streams.
    
           All exec options add the following variables to the child's
           environment:
    
           **NCAT_REMOTE_ADDR** , **NCAT_REMOTE_PORT**
               The IP address and port number of the remote host. In connect
               mode, it's the target's address; in listen mode, it's the
               client's address.
    
           **NCAT_LOCAL_ADDR** , **NCAT_LOCAL_PORT**
               The IP address and port number of the local end of the
               connection.
    
           **NCAT_PROTO**
               The protocol in use: one of TCP, UDP, and SCTP.
    


## ACCESS CONTROL OPTIONS



           **--allow** _host_**[,**_host_ ,...] (Allow connections)
               The list of hosts specified will be the only hosts allowed to
               connect to the Ncat process. All other connection attempts
               will be disconnected. In case of a conflict between **--allow**
               and **--deny** , **--allow** takes precedence. Host specifications
               follow the same syntax used by Nmap.
    
           **--allowfile** _file_ (Allow connections from file)
               This has the same functionality as **--allow** , except that the
               allowed hosts are provided in a new-line delimited allow file,
               rather than directly on the command line.
    
           **--deny** _host_**[,**_host_ ,...] (Deny connections)
               Issue Ncat with a list of hosts that will not be allowed to
               connect to the listening Ncat process. Specified hosts will
               have their session silently terminated if they try to connect.
               In case of a conflict between **--allow** and **--deny** , **--allow**
               takes precedence. Host specifications follow the same syntax
               used by Nmap.
    
           **--denyfile** _file_ (Deny connections from file)
               This is the same functionality as **--deny** , except that excluded
               hosts are provided in a new-line delimited deny file, rather
               than directly on the command line.
    


## TIMING OPTIONS



           These options accept a time parameter. This is specified in
           seconds by default, though you can append ms, s, m, or h to the
           value to specify milliseconds, seconds, minutes, or hours.
    
           **-d** _time_ , **--delay** _time_ (Specify line delay)
               Set the delay interval for lines sent. This effectively limits
               the number of lines that Ncat will send in the specified
               period. This may be useful for low-bandwidth sites, or have
               other uses such as coping with annoying **iptables --limit**
               options.
    
           **-i** _time_ , **--idle-timeout** _time_ (Specify idle timeout)
               Set a fixed timeout for idle connections. If the idle timeout
               is reached, the connection is terminated.
    
           **-q** _time_ (Delay quit after EOF on stdin)
               After EOF on stdin, wait the specified amount of time, then
               quit. If _time_ is negative, wait forever. Ncat may still quit
               based on idle timeout or EOF on the socket.
    
           **-w** _time_ , **--wait** _time_ (Specify connect timeout)
               Set a fixed timeout for connection attempts.
    


## OUTPUT OPTIONS



           **-o** _file_ , **--output** _file_ (Save session data)
               Dump session data to a file
    
           **-x** _file_ , **--hex-dump** _file_ (Save session data in hex)
               Dump session data in hex to a file.
    
           **--append-output**(Append output)
               Issue Ncat with **--append-ouput** along with **-o** and/or **-x** and it
               will append the resulted output rather than truncating the
               specified output files.
    
           **-v** , **--verbose**(Be verbose)
               Issue Ncat with **-v** and it will be verbose and display all
               kinds of useful connection based information. Use more than
               once (**-vv** , **-vvv**...) for greater verbosity.
    


## MISC OPTIONS



           **-C** , **--crlf**(Use CRLF as EOL)
               This option tells Ncat to convert LF line endings to CRLF when
               taking input from standard input.  This is useful for talking
               to some stringent servers directly from a terminal in one of
               the many common plain-text protocols that use CRLF for
               end-of-line.
    
           **-h** , **--help**(Help screen)
               Displays a short help screen with common options and
               parameters, and then exits.
    
           **--recv-only**(Only receive data)
               If this option is passed, Ncat will only receive data and will
               not try to send anything.
    
           **--send-only**(Only send data)
               If this option is passed, then Ncat will only send data and
               will ignore anything received. This option also causes Ncat to
               close the network connection and terminate after EOF is
               received on standard input.
    
           **--no-shutdown**(Do not shutdown into half-duplex mode)
               If this option is passed, Ncat will not invoke shutdown on a
               socket after seeing EOF on stdin. This is provided for
               backward-compatibility with OpenBSD netcat, which exhibits
               this behavior when executed with its '-d' option.
    
           **-n** , **--nodns**(Do not resolve hostnames)
               Completely disable hostname resolution across all Ncat
               options, such as the destination, source address, source
               routing hops, and the proxy. All addresses must be specified
               numerically. (Note that resolution of proxy destinations is
               controlled separately via option **--proxy-dns**.)
    
           **-t** , **--telnet**(Answer Telnet negotiations)
               Handle DO/DONT WILL/WONT Telnet negotiations. This makes it
               possible to script Telnet sessions with Ncat.
    
           **--version**(Display version)
               Displays the Ncat version number and exits.
    


## UNIX DOMAIN SOCKETS



           The **-U** option (same as **--unixsock**) causes Ncat to use Unix domain
           sockets rather than network sockets. Unix domain sockets exist as
           an entry in the filesystem. You must give the name of a socket to
           connect to or to listen on. For example, to make a connection,
    
           **ncat -U ~/unixsock**
    
           To listen on a socket:
    
           **ncat -l -U ~/unixsock**
    
           Listen mode will create the socket if it doesn't exist. The socket
           will continue to exist after the program ends.
    
           Both stream and datagram domain sockets are supported. Use **-U** on
           its own for stream sockets, or combine it with **--udp** for datagram
           sockets. Datagram sockets require a source socket to connect from.
           By default, a source socket with a random filename will be created
           as needed, and deleted when the program ends. Use the **--source**
           with a path to use a source socket with a specific name.
    


## AF_VSOCK SOCKETS



           The **--vsock** option causes Ncat to use AF_VSOCK sockets rather than
           network sockets. A CID must be given instead of a hostname or IP
           address. For example, to make a connection to the host,
    
           **ncat --vsock 2 1234**
    
           To listen on a socket:
    
           **ncat -l --vsock 1234**
    
           Both stream and datagram domain sockets are supported, but socket
           type availability depends on the hypervisor. Use **--vsock** on its
           own for stream sockets, or combine it with **--udp** for datagram
           sockets.
    


## EXAMPLES



           Connect to example.org on TCP port 8080.
               **ncat example.org 8080**
    
           Listen for connections on TCP port 8080.
               **ncat -l 8080**
    
           Redirect TCP port 8080 on the local machine to host on port 80.
               **ncat --sh-exec "ncat example.org 80" -l 8080 --keep-open**
    
           Bind to TCP port 8081 and attach /bin/bash for the world to access
           freely.
               **ncat --exec "/bin/bash" -l 8081 --keep-open**
    
           Bind a shell to TCP port 8081, limit access to hosts on a local
           network, and limit the maximum number of simultaneous connections
           to 3.
               **ncat --exec "/bin/bash" --max-conns 3 --allow 192.168.0.0/24**
               **-l 8081 --keep-open**
    
           Connect to smtphost:25 through a SOCKS4 server on port 1080.
               **ncat --proxy socks4host --proxy-type socks4 --proxy-auth joe**
               **smtphost 25**
    
           Connect to smtphost:25 through a SOCKS5 server on port 1080.
               **ncat --proxy socks5host --proxy-type socks5 --proxy-auth**
               **joe:secret smtphost 25**
    
           Create an HTTP proxy server on localhost port 8888.
               **ncat -l --proxy-type http localhost 8888**
    
           Send a file over TCP port 9899 from host2 (client) to host1
           (server).
               HOST1$ **ncat -l 9899 > outputfile**
    
               HOST2$ **ncat HOST1 9899 < inputfile**
    
           Transfer in the other direction, turning Ncat into a “one file”
           server.
               HOST1$ **ncat -l 9899 < inputfile**
    
               HOST2$ **ncat HOST1 9899 > outputfile**
    


## EXIT CODE



           The exit code reflects whether a connection was made and completed
           successfully. 0 means there was no error. 1 means there was a
           network error of some kind, for example “Connection refused” or
           “Connection reset”. 2 is reserved for all other errors, like an
           invalid option or a nonexistent file.
    


## BUGS



           Like its authors, Ncat isn't perfect. But you can help make it
           better by sending bug reports or even writing patches. If Ncat
           doesn't behave the way you expect, first upgrade to the latest
           version available from **https://nmap.org ******. If the problem persists,
           do some research to determine whether it has already been
           discovered and addressed. Try Googling the error message or
           browsing the nmap-dev archives at**https://seclists.org/ ******.
    
           Read this full manual page as well. If nothing comes of this, mail
           a bug report to <dev@nmap.org>. Please include everything you have
           learned about the problem, as well as what version of Ncat you are
           running and what operating system version it is running on.
           Problem reports and Ncat usage questions sent to dev@nmap.org are
           far more likely to be answered than those sent to Fyodor directly.
    
           Code patches to fix bugs are even better than bug reports. Basic
           instructions for creating patch files with your changes are
           available at **https://svn.nmap.org/nmap/HACKING ******. Patches may be
           sent to nmap-dev (recommended) or to Fyodor directly.


## LEGAL NOTICES



       **Ncat Copyright and Licensing**
           Ncat is (C) 2005–2022 Nmap Software LLC. It is distributed as free
           and open source software under the same license terms as our Nmap
           software. Precise terms and further details are available from
           **https://nmap.org/man/man-legal.html ******.**Creative Commons License for this Ncat Guide**
           This Ncat Reference Guide is (C) 2005–2022 Nmap Software LLC. It
           is hereby placed under version 3.0 of the **Creative Commons**
           **Attribution License******[1]. This allows you redistribute and modify
           the work as you desire, as long as you credit the original source.
           Alternatively, you may choose to treat this document as falling
           under the same license as Ncat itself (discussed previously).**Source Code Availability and Community Contributions**
           Source is provided to this software because we believe users have
           a right to know exactly what a program is going to do before they
           run it. This also allows you to audit the software for security
           holes (none have been found so far).
    
           Source code also allows you to port Nmap (which includes Ncat) to
           new platforms, fix bugs, and add new features. You are highly
           encouraged to send your changes to <dev@nmap.org> for possible
           incorporation into the main distribution. By sending these changes
           to Fyodor or one of the Insecure.Org development mailing lists, it
           is assumed that you are offering the Nmap Project (Nmap Software
           LLC) the unlimited, non-exclusive right to reuse, modify, and
           relicense the code. Nmap will always be available open source, but
           this is important because the inability to relicense code has
           caused devastating problems for other Free Software projects (such
           as KDE and NASM). We also occasionally relicense the code to third
           parties as discussed in the Nmap man page. If you wish to specify
           special license conditions of your contributions, just say so when
           you send them.
    
       **No Warranty**
           This program is distributed in the hope that it will be useful,
           but WITHOUT ANY WARRANTY; without even the implied warranty of
           MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the Nmap
           Public Source License for more details at **https://nmap.org/npsl/ ******,
           or in the LICENSE file included with Nmap.**Inappropriate Usage**
           Ncat should never be installed with special privileges (e.g. suid
           root).  That would open up a major security vulnerability as other
           users on the system (or attackers) could use it for privilege
           escalation.
    
       **Third-Party Software**
           This product includes software developed by the **Apache Software**
           **Foundation******[2]. A modified version of the**Libpcap portable packet**
           **capture library******[3] is distributed along with Ncat. The Windows
           version of Ncat utilized the Libpcap-derived**Npcap library******[4]
           instead. Certain raw networking functions use the**Libdnet******[5]
           networking library, which was written by Dug Song.  A modified
           version is distributed with Ncat. Ncat can optionally link with
           the**OpenSSL cryptography toolkit******[6] for SSL version detection
           support. All of the third-party software described in this
           paragraph is freely redistributable under BSD-style software
           licenses.


## NOTES



            1. Creative Commons Attribution License
               http://creativecommons.org/licenses/by/3.0/
    
            2. Apache Software Foundation
               http://www.apache.org
    
            3. Libpcap portable packet capture library
               http://www.tcpdump.org
    
            4. Npcap library
               https://npcap.com
    
            5. Libdnet
               http://libdnet.sourceforge.net
    
            6. OpenSSL cryptography toolkit
               http://www.openssl.org
    


* * *