Sudden Putty Connection Issue

[djtech2k]

Does this ring any bells?

 

[Digilog]

See if Version 2 is being used in the PUtty.

Also under SSH->auth make sure your username/password auth (keyboard-interactive) is enabled:

If you change anything, be sure to save by clicking the session tab, select Default settings and save.

 

[Martinski]

... When us9ng the v0.82 version of plink, I got the same error as putty so I grabbed v0.81 ...

Well, you didn't really provide all the data points (e.g. the exact error message in context). Don't be afraid to show *all* the data and as much info as possible; do not just describe and comment on it.

When there are several moving parts involved, we don't know which data may be important and which is not, or what could be a relevant clue, and what's irrelevant until we look at it in the proper context. By not providing as much data as requested, we only get small pieces of the puzzle (it's like trying to watch a movie through a straw), and I don't feel like pulling teeth this evening.

 

[John Fitzgerald]

I don't feel like pulling teeth this evening.

Why would you want to waste your precious time on this?
AC68U
384 code base and won't update
replacing router in a couple of weeks

 

[Digilog]

Plink is not designed to be used as a console interface. Therefore, it does not output to stout to ask for the username/passowrd.
Plink can use PUtty's saved connections. But the connection profile in PUtty has to be saved properly.

Use a regular SSH console and plink for scripts.

Internet facing SSH should always use key based authentication.

 

[Digilog]

Why would you want to waste your precious time on this?
AC68U
384 code base and won't update
replacing router in a couple of weeks

It is one the reasons why I run a server as my router and these store bought routers as access points.

But I will tell you now, most, if not all, store bought routers are not engineered well in the first place and their planned obsolescence reflects how well they stand behind their design.

Next router I purchase will be a banana pi router kit. At least I know how to construct it into an enclosure so it doesn't overheat and I don't have to be stuck with anyone's buggy firmware and low end software.

 

[djtech2k]

See if Version 2 is being used in the PUtty.

View attachment 62901

Also under SSH->auth make sure your username/password auth (keyboard-interactive) is enabled:

View attachment 62902

If you change anything, be sure to save by clicking the session tab, select Default settings and save.

I checked and both of those options are set that way in the profile.

 

[ColinTaylor]

Plink is not designed to be used as a console interface. Therefore, it does not output to stout to ask for the username/passowrd.

It does actually. And with the verbose option it outputs more information to stdout, as seen in post #40.

C:\>plink 192.168.1.1
login as: admin
admin@192.168.1.1's password:

Access granted. Press Return to begin session.



ASUSWRT-Merlin RT-AX86U 3004.388.7_0 Fri Apr 26 18:22:46 UTC 2024
admin@RT-AX86U:/tmp/home/root#

 

[djtech2k]

Well, you didn't really provide all the data points (e.g. the exact error message in context). Don't be afraid to show *all* the data and as much info as possible; do not just describe and comment on it.

When there are several moving parts involved, we don't know which data may be important and which is not, or what could be a relevant clue, and what's irrelevant until we look at it in the proper context. By not providing as much data as requested, we only get small pieces of the puzzle (it's like trying to watch a movie through a straw), and I don't feel like pulling teeth this evening.

I think the only thing I did not provide was the output from the failed plink v0.82. I thought the point was to show the successful output so I posted all of that. Here is the output from the plink v0.82 error:

Looking up host "192.168.x.x" for SSH connection
Connecting to 192.168.x.x port 22
We claim version: SSH-2.0-PuTTY_Release_0.82
Connected to 192.168.x.x (from 192.168.x.y:49152)
Remote version: SSH-2.0-dropbear
Using SSH protocol version 2
Doing ECDH key exchange with curve Curve25519, using hash SHA-256 (SHA-NI accelerated)
Network error: Software caused connection abort
FATAL ERROR: Network error: Software caused connection abort

Is there something else I am missing that I did not include? I re-read your post and I have 100% of the output from the commands you mentioned.

 

[Digilog]

I think the only thing I did not provide was the output from the failed plink v0.82. I thought the point was to show the successful output so I posted all of that. Here is the output from the plink v0.82 error:

Looking up host "192.168.x.x" for SSH connection
Connecting to 192.168.x.x port 22
We claim version: SSH-2.0-PuTTY_Release_0.82
Connected to 192.168.x.x (from 192.168.x.y:49152)
Remote version: SSH-2.0-dropbear
Using SSH protocol version 2
Doing ECDH key exchange with curve Curve25519, using hash SHA-256 (SHA-NI accelerated)
Network error: Software caused connection abort
FATAL ERROR: Network error: Software caused connection abort

Is there something else I am missing that I did not include? I re-read your post and I have 100% of the output from the commands you mentioned.

Plink is to be used in a batch file. Why are you trying to use it as a console interface?

Since you load a connection profile from PUtty into it, does the saved PUtty connection session work?

 

[djtech2k]

I am only using plink as requested from @Martinski to see the output.

I do not normally use plink but in my experience using it for this thread, it does connect in an interactive session. When I issue the connect command, it prompts me for password and I get to an interactive session where I can run commands, just like I would in an SSH session. In my case, I did not load any kind of putty connection session. I specified the IP, port, and username on the command-line and it interactive prompts for the password, which I enter. That puts me at an active SSH prompt where I can run whatever commands I want.

 

[Martinski]

Plink is not designed to be used as a console interface. Therefore, it does not output to stout to ask for the username/passowrd.
...

You’re completely wrong about that. The plink executable is PuTTY's CLI tool, and it's designed for both interactive and automated logins. Although it's typically/primarily used for automated operations, there's nothing that prevents you from using it for interactive sessions.

You should try the plink command for yourself to remove any lingering doubts before posting next.

 

[Martinski]

Why would you want to waste your precious time on this?
AC68U
384 code base and won't update
replacing router in a couple of weeks

I get where you're coming from & understand your point of view. For me, it's more of an academic exercise, and being very curious, I'd just like to understand why PuTTY v0.82 fails while v0.81 succeeds. OTOH, after a long day at work yesterday, I didn’t feel like "pulling teeth" WRT getting the requested output from the OP.

 

[Martinski]

I think the only thing I did not provide was the output from the failed plink v0.82. I thought the point was to show the successful output so I posted all of that.

Part of the request for further data was to get the errors generated during the initial SSH connection handshake:

Since the reported issue appears to be between your laptop running PuTTY v0.82 and your router’s Dropbear SSH server, and the system log on the server side indicates there's an error during the key exchange when trying to connect, I recommend running the PuTTY CLI executable in verbose mode to see what errors are being generated on the client side.
...

In any case, thanks for the additional data. I'll take a closer look tomorrow evening. I don't have much time tonight.

Here is the output from the plink v0.82 error:

Looking up host "192.168.x.x" for SSH connection
Connecting to 192.168.x.x port 22
We claim version: SSH-2.0-PuTTY_Release_0.82
Connected to 192.168.x.x (from 192.168.x.y:49152)
Remote version: SSH-2.0-dropbear
Using SSH protocol version 2
Doing ECDH key exchange with curve Curve25519, using hash SHA-256 (SHA-NI accelerated)
Network error: Software caused connection abort
FATAL ERROR: Network error: Software caused connection abort

Is there something else I am missing that I did not include? I re-read your post and I have 100% of the output from the commands you mentioned.

 

[Martinski]

... Here is the output from the plink v0.82 error:

Looking up host "192.168.x.x" for SSH connection
Connecting to 192.168.x.x port 22
We claim version: SSH-2.0-PuTTY_Release_0.82
Connected to 192.168.x.x (from 192.168.x.y:49152)
Remote version: SSH-2.0-dropbear
Using SSH protocol version 2
Doing ECDH key exchange with curve Curve25519, using hash SHA-256 (SHA-NI accelerated)
Network error: Software caused connection abort
FATAL ERROR: Network error: Software caused connection abort

Well, my curiosity won so I took a look at your latest output. It shows that the key exchange seems to have been negotiated between the Dropbear server & the v0.82 client (ECDH key exchange: curve25519-sha256 - the same KEX algorithm that works with OpenSSH & v0.81 clients), but the connection was then immediately aborted so it never gets to negotiate the Host key algorithm.

Can you post a screenshot for each of the following PuTTY v0.82 GUI windows *after* loading the session you have configured and used to connect to the router?

1) Connection
2) Connection ---> SSH ---> Kex
3) Connection ---> SSH ---> Host keys
4) Connection ---> SSH ---> Cipher

On the "Connection" window (1), put a checkmark on the option to "Enable TCP keepalives" and set the number of seconds between "keepalives" to 5. Make sure to go back to the top "Session" window and click on "Save" to store the changes in the current session name.

This is pure speculation, but this type of sudden abort reminded me of cases where the connection was being terminated because there were no keepalives. I wouldn't think this is the case here at the early stage, but since your Dropbear version is very old, perhaps there are issues in that version related to keepalives.

Once you have saved the modified SSH session configuration, run the following command on a Windows Command Prompt terminal:

plink -v "My_SSH_Session"

Where "My_SSH_Session" is the name given to your PuTTY SSH configuration to connect to the router webGUI.

Then post the resulting output.

 

[John Fitzgerald]

@Martinski

Have you looked at the PuTTY change log for clues, maybe v0.77 forward.

PuTTY Change Log

www.chiark.greenend.org.uk

 

[djtech2k]

Here are the screenshots from putty that you requested.

Here is the result of the plink command that you asked about, after saving the profile with the keepalive settings.

Looking up host "192.168.x.x" for SSH connection
Connecting to 192.168.x.x port 22
We claim version: SSH-2.0-PuTTY_Release_0.82
Connected to 192.168.x.x (from 192.168.x.y:60139)
Remote version: SSH-2.0-dropbear
Using SSH protocol version 2
Doing ECDH key exchange with curve Curve25519, using hash SHA-256 (SHA-NI accelerated)
Network error: Software caused connection abort
FATAL ERROR: Network error: Software caused connection abort

 

[Digilog]

You’re completely wrong about that. The plink executable is PuTTY's CLI tool, and it's designed for both interactive and automated logins. Although it's typically/primarily used for automated operations, there's nothing that prevents you from using it for interactive sessions.

You should try the plink command for yourself to remove any lingering doubts before posting next.

Please read the notes from the author:
from https://github.com/github/putty/blob/master/doc/plink.but

\C{plink} Using the command-line connection tool \i{Plink}

\i{Plink} is a command-line connection tool similar to UNIX \c{ssh}.
It is mostly used for \i{automated operations}, such as making CVS
access a repository on a remote server.

Plink is probably not what you want if you want to run an
\i{interactive session} in a console window.

Yes you could run it as a console environment once you set it up. But you have to set up the connection profile or invoke it on the command line.
I'm just glad I don't have to use toy programs like this for SSH anymore since I primarily use Linux.

 

[KevTech]

No issues with Putty .82 with router in sig or XT12.

 

[Martinski]

@Martinski

Have you looked at the PuTTY change log for clues, maybe v0.77 forward.

PuTTY Change Log

www.chiark.greenend.org.uk

Yeah, one of the first things I did was read the changelogs for v0.81 & v0.82 releases. Since v0.81 works fine for the OP, it’s odd that v0.82 fails almost immediately. But I know better than to rely solely on changelog bullet points. The only way to get the nitty-gritty details of the code changes and understand their impact is to look at the source code commits, but that’s beyond the scope here and exceeds the time I’m willing to spend on this academic exercise.