[GLLUG] Netcat Bash prompt

[Michael P. Flaga]

The windows machine’s program will initiate a telnet to something (likely the Linux Box)? Where the linux jump box is only (initially) accepting SSH. Telnetd has been removed and 23 been block, even from local access.

 

So the idea is to get netcat (-t for telnet emulation), on some other port, to pipe to and from bash. As to emulate a Telnet on the linux box. Noting that telnetd has been removed.  So that the Telnet client can either connect directly to the linux box’s netcat –t port. Or through a tunnel to it, if needed. Which does not appear to be needed, as I can netcat directly between the two machines on any port other than 22 (being used) and 23(blocked), as the rest are allowed.

 

Michael P. Flaga, michael at flaga.net

 

From: Daniel Griswold [mailto:daniel at griswoldcomputing.com] 
Sent: Thursday, December 04, 2014 5:08 PM
To: michael at flaga.net
Cc: 'Jason L. Froebe'; 'GLLUG'
Subject: Re: [GLLUG] Netcat Bash prompt

 

"ssh $jumpserver ssh $targetserver /bin/bash -i" will give the client an interactive session on the target server

if using ssh keys/agents to not require interactive authentication, you can do:

echo "command" | ssh $jumpserver ssh $targetserver /bin/bash

which will run the command on the remote host and return when the process on the remote host terminates.

I'm confused as to whether the connections are initiating to terminating at the linux servers.  The Windows implementation may not support the above.

--Daniel

 

On 2014-12-04 16:22, Michael P. Flaga 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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