Is there a way to quickly bind to a TCP port/ip address and simply print out all information to STDOUT? I have a simple debugging solution which writes things to 127.0.0.1:4444 and I'd like to be able to simply bind up a port from bash and print everything that comes across. Is there an easy way to do this?
$ nc -k -l 4444 > filename.out
see nc(1)
Just because you asked how to do it in bash, though netcat answer is very valid:
$ exec 3<>/dev/tcp/127.0.0.1/4444
$ cat <&3
That is working as you expecting:
nc -k -l 4444 |bash
and then you
echo "ls" >/dev/tcp/127.0.0.1/4444
then you see the listing performed by bash.
[A Brief Security Warning]
Of course if you leave a thing like this running on your computer, you have a wide open gateway for all kinds of attacks because commands can be sent from any user account on any host in your network. This implements no security (authentication, identification) whatsoever and sends all transmitted commands unencrypted over the network, so it can very easily be abused.
Adding an answer using ncat that #Freedom_Ben alluded to:
ncat -k -l 127.0.0.1 4444
and explanation of options from man ncat:
-k, --keep-open Accept multiple connections in listen mode
-l, --listen Bind and listen for incoming connections
Related
I am trying to understand why netcat listener isn't working in my Kali Linux VM. From what I understand,I open a terminal and open the port.
nc -l 155
Then, I open another terminal within my VM and use the following command to connect to that port number.
nc 127.0.0.1 155 (loopback IP address and same port number)
It was unsuccessful and since I am just a newbie in this field, I was hoping to get some assistance on this issue. However, I found a new way to execute this command but I am not understanding the logic behind why this new way works and not the original method that I learned in class. Thank you for your help in advance!
First of all, to elevate your self from newbie status, you have to understand what errors mean. "it was unsuccessful" is an insufficient description of your results for any real debugging. Probably, what happened was a valuable clue to the issue - you should have included that information. Furthermore, you really have to get your commands in the quetsion exactly right. Don't say you did one thing, then post a screenshot of something else happening. I'm not sure what the -e is supposed to be doing, but I don't find any record of it in my osx implementation or online man pages.
Different builds or implementations of netcat could differ, but from what I'm seeing from a netcat on my osx box, -p is not the right way to specify destination port.
$ nc localhost -p 1055
nc: missing hostname and port
usage: nc [-46AacCDdEFhklMnOortUuvz] [-K tc] [-b boundif] [-i interval] [-p source_port] [--apple-delegate-pid pid] [--apple-delegate-uuid uuid]
[-s source_ip_address] [-w timeout] [-X proxy_version]
[-x proxy_address[:port]] [hostname] [port[s]]
-p specifies source port. You don't usually need to specify this. Furthermore, you can't have a source and destination of the socket on the same box on the same port. Usually source port doesn't need to be specified.
Finally, ports under 1024 can only be allocated as root. Like most linux professionals, I don't run anything as root unless I really have to, so I changed to 1055 for this demonstration. One nc each in a termina window, typing messages in one print out the other side. Observe:
$ nc -l 1055
hi world
hi yourself, world!
$ nc localhost 1055
hi world
hi yourself, world!
server: nc -l ${port} > ${file}
local: nc ${ip} -z ${port} < ${file}
On RHEL 7.2 OS, I get following error when trying to run nc commnad
nc -z -v -w1 host port
nc: invalid option -- 'z'
Ncat: Try `--help' or man(1) ncat for more information, usage options and help. QUITTING.
Is there any alternative to it
maybe nc is a link to ncat, use the commands to checkļ¼
which nc | xargs ls -l
if the nc is linked to ncat,you should relink nc to netcat, if netcat is not installed, refer the website:http://netcat.sourceforge.net/download.php
It seems the old version of nc is being phased out everywhere in favour of Nmap Ncat. Unfortunately this doesn't have the rather useful -z option.
One way to get equivalent functionality (test whether the target host is listening on a given port) is to transform this:
nc -z hostname port
Into this:
cat /dev/null | nc hostname port
You might also want to add in an option like -w 1s to avoid the long default timeout.
There might be a cleaner combination of options that avoids the need for the /dev/null but I couldn't figure out what.
I've also seen talk of using tcping to do the same thing, but that doesn't seem to be available on all distros.
On the newer RHEL 7 nc is a link to ncat, while you may be used to nc on the older RHEL6 and below.
ncat seems not to have the -z option, and being a different project having a look at it's man page is a good idea, or at least examine it's internal help
ncat -h
I am using netcat utility on linux to receive outputs from a program on a windows machine. My problem being that the program on the windows machine does not always give an output.
How can i check that either a connection has been made to netcat ?
What i am doing till now is "nc -l -v 9103 > output" then i check the size of output, the problem this poses is that netcat only write to a file after a certain buffer size has been reached or a new line char is encountered, so some cases evne though a connection has been made the file size is detected as zero.
How can i check if someone has made a connection with netcat.
I tried using
nc -l -v -e someprog.exe 9103 > output
but my netcat doesnt seem to support this
below are the options i have
$ nc -h
usage: nc [-46DdhklnrStUuvzC] [-i interval] [-p source_port]
[-s source_ip_address] [-T ToS] [-w timeout] [-X proxy_version]
[-x proxy_address[:port]] [hostname] [port[s]]
Command Summary:
-4 Use IPv4
-6 Use IPv6
-D Enable the debug socket option
-d Detach from stdin
-h This help text
-i secs Delay interval for lines sent, ports scanned
-k Keep inbound sockets open for multiple connects
-l Listen mode, for inbound connects
-n Suppress name/port resolutions
-p port Specify local port for remote connects
-r Randomize remote ports
-s addr Local source address
-T ToS Set IP Type of Service
-C Send CRLF as line-ending
-t Answer TELNET negotiation
-U Use UNIX domain socket
-u UDP mode
-v Verbose
-w secs Timeout for connects and final net reads
-X proto Proxy protocol: "4", "5" (SOCKS) or "connect"
-x addr[:port] Specify proxy address and port
-z Zero-I/O mode [used for scanning]
Port numbers can be individual or ranges: lo-hi [inclusive]
verbose mode will write connectivity to stderr, and you can redirect stderr to a file, the verbose log has something like
connect to [xxx] from [xxxx]
try
nc -l -v -p 9103 -k 1> output 2>connect.log
and monitor connect.log for connectivity
if you don't use -k , netcat quits after 1st connection.
If you can upgrade your copy of netcat: the modern versions (1.10, for one) have an option to execute a program (or a shell command) upon connect. Otherwise, you can make the netcat think it runs in a terminal (to disable buffering of stdout), by using for example script (it just saves everything on stdin/stdout/stderr in the given file). Or use logging features of screen and tmux.
I want to combine "chat" and "nc" on linux, so I will create a tiny udp server that responds on a specific request and sends back an answer.
In fact I want to redirect the stdout of "nc" to the stdin of "chat" and vice versa. My first attempt was:
nc -w 3000 -u -n -l -p 30000 >&1111 <2222 &
chat -V 'request' 'answer' >&2222 <1111
But it didn't work.
use socat instead of netcat. Something like this :
socat UDP-LISTEN:5555 EXEC:"chat -sv ping pong",pty
To test it, you can open another terminal, and use socat to bridge stdio and an UDP socket :
socat - UDP:localhost:5555
Type ping, and you will get pong !
Assume a legacy Linux application listening on a UNIX domain socket /tmp/foo.
In addition to communicating with this legacy application over the UNIX domain socket mechanism I want to be able to connect to it via a TCP-connection on port say 1234.
What is the easiest way to bind to TCP port 1234 and then redirect all incoming connections to the UNIX domain socket /tmp/foo?
Turns out socat can be used to achieve this:
socat TCP-LISTEN:1234,reuseaddr,fork UNIX-CLIENT:/tmp/foo
And with a bit of added security:
socat TCP-LISTEN:1234,bind=127.0.0.1,reuseaddr,fork,su=nobody,range=127.0.0.0/8 UNIX-CLIENT:/tmp/foo
These examples have been tested and work as expected.
Easiest? Probably Netcat (aka nc):
nc -l 1234 | nc -U /tmp/foo
The first command listens on port 1234 for incoming connections, and pipes the resulting data to the second command. The second connects to the Unix domain socket /tmp/foo, and writes its input to that socket. Note that this will only accept a single connection, and exit as soon as that connection is dropped. If you want to keep listening for more connections, use the -k option:
nc -lk 1234 | nc -U /tmp/foo
You can test that this is working by setting up a listener for that socket in one terminal:
nc -lUk /tmp/foo
And writing to it in another:
nc localhost 1234
socat, as recommended by knorv, is more capable, but more complicated to use.
You should be able to bind to TCP 1234, get a socket fd for /tmp/foo and use the select call to 'listen' for data on both 1234, and /tmp/foo. Any data written to 1234, you rewrite to /tmp/foo and vice-versa.
You now act as a proxy and transfer data back and forth.
And here is a web-page which might help: http://osr507doc.sco.com/en/netguide/dusockC.io_multiplexing.html
In additons to #knorv's answer: with xinetd it can work like a daemon
# cat /etc/xined.d/mysrv
service mysrv
{
disable = no
type = UNLISTED
socket_type = stream
protocol = tcp
wait = no
server = /usr/bin/socat
server_args = STDIN UNIX-CLIENT:/tmp/mysocket.sock
bind = 127.0.0.1
port = 1234
}
Not tried it : but it looks like 'lighttpd' can do this for you:
http://redmine.lighttpd.net/wiki/lighttpd/Docs:ModProxyCore