I connect to a Linux machine (CentOS 6.4) using PuTTY. Except from fact that I can set PuTTY to only use one type of protocol, how can I find the current SSH connection's version (SSH1 or SSH2)?
An alternative way.
As cstamas suggested, you can use
ssh -v localhost. Uou simply ssh to yourself 127.0.0.1 on verbose mode, which will display debugging messages of the progress. Yes, through this process you can look at the top of the communication and you can get the SSH version that you are currently running.
But if you read the
ssh man page, you will find the
-V option on
ssh more useful. Taken out the
ssh man page:
-V Display the version number and exit.
-v Verbose mode. Causes ssh to print debugging messages about its progress. This is helpful in debugging connection, authentication, and configuration problems. Multiple -v options increase the verbosity. The maximum is 3.
So I think it would be better to simply do
ssh -V and get something similar to:
> ssh -V OpenSSH_6.6.1p1, OpenSSL 1.0.1e-fips 11 Feb 2013
In Session, Logging, select the "SSH packets and raw data" radio button. Select the log file as putty.log in a location of your choice. Make the connection. You should see:
Event Log: Server version: SSH-2.0-OpenSSH_5.3 Event Log: Using SSH protocol version 2
See below for details on what SSH-2.0 means.
You could also try using the telnet client, but point to port 22:
telnet test1 22
When you connect you will see:
Connected to test1.
Escape character is '^]'.
The last line is the one to look for:
If it says
SSH-2.0 then that is good, the SSH server you connected to supports only SSH protocol version 2. It will not support connections from SSH V1 protocol clients.
If however you see:
Then that means that the server end is still supporting SSH protocol version 1. It has something like this in it's
Protocol 1 is vulnerable and should not be used.
So to get that straight. If you see SSH-2 when you telnet to port 22 of the remote server then you can only be using SSH protocol version 2 as the server does not support protocol 1.
As per cstamas answer above, the
-v flag will show a line:
debug1: Remote protocol version 1.99, remote software version OpenSSH_5.3
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.3
You want to see
version 2.0 there.
To get more details you can use this:
rpm -qi openssh
Name : openssh Version : 7.4p1 Release : 21.el7 Architecture: x86_64 Install Date: Пт 17 янв 2020 12:21:57 Group : Applications/Internet Size : 1991172 License : BSD Signature : RSA/SHA256, Пт 23 авг 2019 00:37:23, Key ID 24c6a8a7f4a80eb5 Source RPM : openssh-7.4p1-21.el7.src.rpm Build Date : Пт 09 авг 2019 04:40:49 Build Host : x86-01.bsys.centos.org Relocations : (not relocatable) Packager : CentOS BuildSystem <http://bugs.centos.org> Vendor : CentOS URL : http://www.openssh.com/portable.html Summary : An open source implementation of SSH protocol versions 1 and 2
The only method I am aware of requires that one has sufficient privileges to view the
ssh log entries in
$ echo $SSH_CONNECTION 127.0.0.1 12375 127.0.0.1 22
The first and second fields of the
SSH_CONNECTION variable indicate the source IP address and source port of my connection. By
grep-ing for those values in
/var/log/auth.log, I can find the log entry from when my SSH connection was authenticated.
$ sudo grep -F ' from 127.0.0.1 port 12375 ' /var/log/auth.log | grep ssh Jun 26 16:29:52 morton sshd: Accepted keyboard-interactive/pam for jim from 127.0.0.1 port 12375 ssh2
This log entry tells me that my current connection is using the SSH 2 protocol. Of course, if the
ssh session has been open for several days, the log entry may be in
/var/log/auth.log.0 or some older