Re: ncat exec or sending a one-shot login string

[Daniel Miller <bonsaiviking () gmail com>]

Brian,

We've fixed a lot of these socket, pipe, and stdin EOF handling issues in
recent versions. Most recently in version 7.00, we added an option that
some folks needed for cron scripts, --no-shutdown, which prevents Ncat from
closing the network connection when it receives EOF on STDIN. Other
relevant options (which may or may not help your particular situation) are:

-k or --keep-open, accept multiple connections in listen mode
--send-only, only send data, ignoring received; quit on EOF
--recv-only, Only receive data, never send anything

Finally, sometimes you need to give Ncat some extra time to receive a
reply, especially with UDP communication. For example this will fail:

echo -ne '\0\x06\x01\0\0\x01\0\0\0\0\0\0\x07version\x04bind\0\0\x10\0\x03'
| ncat -u 192.168.1.1 53

But this will succeed:

(echo -ne
'\0\x06\x01\0\0\x01\0\0\0\0\0\0\x07version\x04bind\0\0\x10\0\x03'; sleep 5)
| ncat -u 192.168.1.1 53

We don't yet have a command option for that, but a subshell+sleep works
pretty well.

Dan

On Sun, Dec 13, 2015 at 9:02 AM, Brian Franklin <brian.is.still () gmail com>
wrote:

> Hi there!  I'm a big fan of ncat, particularly the ssl support.  Well done!
>
> Recently, I'm trying to use it from within cron.  I can't seem to get it
> to work.  Basically, I connect as a client and then pass a login string to
> a remote server, and then it streams some data to me, which I then pipe to
> another process.  I use something like:
>
> cat "login" - | ncat -C --ssl [server] [port] | [some other script]
>
> This works perfectly from the command line (it always does...) but the
> cron job won't work.  Turning up the verbosity provides some interesting
> clues, but I don't know how to interpret most of it.  I've applied all my
> standard "tricks" for debugging a cron job, but I'm getting nowhere.  The
> closest I've come is that it might be related to my use of 'cat' and it's
> reliance on stdin to 'hold' the pipe open?
>
> If I remove the last pipe, and just collect the ncat output using the MTA
> from cron, then it reports a successful connection, but it just seems to
> quit after that.
>
> What I'm trying to achieve is this:
>
> 1.  Connect to remote server
> 2.  Send login string (really just an identity)
> 3.  Receive data
> 4.  Pipe data to another script for processing
>
> Sending the login string is a one-shot deal; after that it's all
> uni-directional communication and I don't send anything back.  I have no
> control over the remote server.
>
> Using ncat 6.40 on Ubuntu 14.04.
>
> Can anyone point me in the right direction?
>
> Thanks,
>
> Brian
>
> _______________________________________________
> Sent through the dev mailing list
> https://nmap.org/mailman/listinfo/dev
> Archived at http://seclists.org/nmap-dev/
_______________________________________________
Sent through the dev mailing list
https://nmap.org/mailman/listinfo/dev
Archived at http://seclists.org/nmap-dev/