[GLLUG] Netcat Bash prompt

[Michael P. Flaga]

Authentication aside. The client app is only Telnet. So it must get terminated (somehow) at the Linux box with Telnet to a bash.

 

If need, it can be more secure by using a ssh tunnel between boxes and configuring the local telnet client to the tunnel. 

 

Michael P. Flaga, michael at flaga.net

 

From: Jason L. Froebe [mailto:jason.froebe at gmail.com] 
Sent: Thursday, December 04, 2014 5:18 PM
To: Michael Flaga
Cc: GLLUG
Subject: Re: [GLLUG] Netcat Bash prompt

 

A big problem with the netcat method is that it doesn't have authentication.  If you can restrict the access to the port via a firewall so access is granted only from a single source, it wouldn't be as bad but the ip address could be spoofed.  A direct physical connection would provide a secure-ish solution to that.

Whether you use a ssh tunnel or netcat, it amounts to the same (a proxy).  With the ssh tunnel, it is far more secure.

jason

 

On Thu, Dec 4, 2014 at 4:22 PM, Michael P. Flaga <michael at flaga.net> wrote:

Yes, I can create a tunnel over, but not forwarded onto another IP, rather need a bash prompt. So that the telneting  program can call bash commands at the remote linux box.

 

The goal is to not simply tunnel the telnet. But rather translate it. Noting that telnetd is gone from the remote linux box. 

 

Netcat is there, so “-t” will answer TELNET negotiation in place of telnetd.

 

Michael P. Flaga, michael at flaga.net

 

From: Jason L. Froebe [mailto:jason.froebe at gmail.com] 
Sent: Thursday, December 04, 2014 4:12 PM
To: Michael Flaga
Cc: GLLUG
Subject: Re: [GLLUG] Netcat Bash prompt

 

On the windows box, use putty to create a ssh tunnel to your Linux box.  This way nothing is transferred unencrypted over the network.  

Jason

On Dec 4, 2014 4:02 PM, "Michael P. Flaga" <michael at flaga.net> wrote:

I have closed source programs that telnet on windows boxes. Where I am constrained to Linux Jump servers. That now only have SSH. The Telnet is GONE on the jump servers. The closed source programs once connected (formerly via telnet) to the jump servers then know who to issue the commands to ssh into the remote targets.

 

I need a way to translate Telnet to SSH on the jump servers.

 

The netcat on the jump servers do not have the –e option, so I cannot run nc in telnet mode into /bin/bash. 

 

I have found 

 

mkfifo pipe_name_in

mkfifo pipe_name_out

nc -l 5555 < pipe_name_out | /bin/bash > pipe_name_in

 

which kind of works. However, the Standard Error does not go down the pipe. 

So I don’t get any echo or prompts, only the response.

 

nc -l 5555 < pipe_name_out | /bin/bash 2> pipe_name_in

does get the some of the prompts but then no responses.

 

nc -l 5555 < pipe_name_out | /bin/bash 2>&1 pipe_name_in

fails to allow connections.

 

Any suggestions or solutions?

 

Michael P. Flaga, michael at flaga.net

 


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