nc

!node

Porting Netcat in Node.js. CLI util. :computer:

To embed it in your Node.js app use the netcat package instead. This is meant to be used as a standalone tool, but it's not fully equal to the original implementation of netcat.

| Linux | Mac OS | Windows |
|-------|--------|---------|
| :white_check_mark: | :white_check_mark: | :white_check_mark: |

What you can do

- [x] TCP & UDP
- [x] Backdoor (Reverse Shell)
- [x] Honeypot
- [x] File transfer
- [x] Port forwarding
- [ ] Proxy
- [x] Web Server & HTTP Client
- [x] Port scanning

Install

$ npm install -g nc

Usage

$ nc -l -p port [- options] [hostname] [port]

Available options:

``
-c shell commands as -e’; use /bin/sh to exec [dangerous!!]
-e filename program to exec after connect [dangerous!!]
-b allow broadcasts
-h this cruft
-i secs delay interval for lines sent, ports scanned
-k set keepalive option on socket
-l listen mode, for inbound connects
-n numeric-only IP addresses, no DNS
-o file hex dump of traffic
-p port local port number
-r randomize local and remote ports
-s addr local source address
-u UDP mode
-U Listen or connect to a UNIX domain socket
-v verbose
-w secs timeout for connects and final net reads (client-side)
-z zero-I/O mode [used for scanning]
``

#### Server: Listen for inbound

$ nc -l -p 2389

#### Client mode

$ nc localhost 2389

Opening a raw connection to port 2389.

#### Transfer file

| Server side | Client side |
|---------------------|------------------------------------|
| nc -l 2389 > test | cat testfile | nc localhost 2389 |

#### Timeout support

$ nc -w 10 localhost 2389

Connection above would be terminated after 10 seconds.

#### Force netcat server to stay up

$ nc -kl 2389

In this way the server remains up even if the client got disconnected.

#### Netcat execute

A far more exciting thing to do is to get a quick shell going on a remote machine by using the -l or listen option and the -e or execute option. When a connection is made, Netcat executes the program of your choice and connects the stdin and stdout of the program to the network connection.

$ nc -l -p 23 -e /bin/sh

#### Retrieve a website Homepage

Let's create a HTTP request file get.txt that contains the following line and then a blank
line:

`
GET / HTTP/1.0

`

To use Netcat to retrieve the home page of a web site use:

$ nc -v www.website.com 80 < get.txt

You will see Netcat make a connection to port 80, send the text contained in the file get.txt, and then output the web server's response to stdout.

#### Configure netcat client to retry on disconnect

In a normal scenario, if the nc client disconnect, it will not retry the connection.
With the --retry or -R param, it will retry the connection after tot seconds.

$ nc -R 5 localhost 2389

#### Unix socket file

If you have docker, let's try to list our containers' images connecting to the docker unix socket file:

`sh
$ echo -e "GET /images/json HTTP/1.0\r\n" | nc -U /var/run/docker.sock
`

PS. for this example root permissions are required: sudo su.

#### Netcat as a Proxy

`sh
$ mkfifo /tmp/fifo
$ nc -l -k -p 8080 /tmp/fifo
`

#### Netcat as a simple port scanner

$ nc -z 192.168.1.100 1-255

#### Dump hex traffic

If you use the -o option you can dump all hex traffic.

$ nc 127.0.0.1 4445 -o /tmp/log.txt

#### UDP Protocol

By default all the sockets that nc utility creates are TCP protocols but this utility also works with UDP protocol. To enable UDP protocol the -u flag is used.

| Server side | Client side |
|---------------------|------------------------------------|
| nc -u -l -p 2389 | nc -u localhost 2389 |

#### Send a UDP message

$ echo 'message' | nc -w 1 -u 192.168.1.111 514

Pipe via UDP (-u) with a wait time (-w) of 1 second to 192.168.1.111 on port 514.

DEBUG

Debug matches the verbose mode.
You can enable it with the -v param or the env var DEBUG=nc. This module uses the node implementation of netcat under the hood, to debug both use: DEBUG=netcat:*,nc`.

Author

Rocco Musolino (@roccomuso)