Testing active ssh keys on the local network

Question

I am trying to complete my bash script in order to find which SSH servers on LAN are still active with the ssh keys, but i am frozen at this step:

#!/bin/bash

# LAN SSH KEYS DISCOVERY SCRIPT

</etc/passwd \
grep /bin/bash |
cut -d: -f6 |
sudo xargs -i -- sh -c '
     [ -e "$1" ] && cat "$1"
' -- {}/.ssh/known_hosts |
cut -d' ' -f1 |
tr ',' '\n' |
sed '
     /^\[/{
          s/\[\(.*\)\]:\(.*\)/\1 \2/;
          t;
     };
     s/$/ 22/;
' |
sort -u |
xargs -l1 -- sh -c '
    if echo "~" | nc -q1 -w3 "$1" "$2" | grep -q "^SSH"; then
          echo "#### SUCCESS $1 $2";
    else
          echo "#### ERROR $1 $2";
    fi
' --

# TIME TO TEST WHICH SSH servers are still active with the SSH keys
# AND THIS IS WHERE I AM FROZEN...
# Would love to have bash script that could
# ssh -l $users_that_have_/bin/bash -i $ssh_keys $ssh_servers
# Would also be very nice if it could save active
# SSH servers with the valid keys in output.txt in the format
# username:local-IP:/path/to/SSH_key

there is also another one simpler to read (but with some temp files getting created):

#!/bin/bash

# LAN SSH KEYS DISCOVERY SCRIPT
# TRYING TO FIND THOSE SSH KEYS NOW

cat /etc/passwd | grep /bin/bash > bash_users
cat bash_users | cut -d ":" -f 6 > cutted.bash_users_home_dir
for bash_users in $(cat cutted.bash_users_home_dir)
do
ls -al $bash_users/.ssh/*id_* >> ssh-keys.txt
done

# DISCOVERING THE KNOWN_HOSTS NOW

for known_hosts in $(cat cutted.bash_users_home_dir)
do
cat $bash_users/.ssh/known_hosts | awk '{print $1}' | sort -u >> 
hosts_known.txt
sleep 2
done
hosts_known=$(wc -l hosts_known.txt)
echo "We have $hosts_known known hosts that could be still active via SSH 
keys"

# TIME TO TEST WHICH SSH servers are still active with the SSH keys
# AND THIS IS WHERE I AM FROZEN...
# Would love to have bash script that could
# ssh -l $users_that_have_/bin/bash -i $ssh_keys $ssh_servers
# Would also be very nice if it could save active
# SSH servers with the valid keys in output.txt in the format
# username:local-IP:/path/to/SSH_key

So right now, as stated in the bash script above, I am trying to find how to do some sort of a ssh -l $users_that_have_/bin/bash -i $ssh_keys $ssh_servers and dump the positive logins in an output.txt file in the following format:

username:local-IP:/path/to/SSH_key

---

To answer DopeGhoti comment:

I'm now trying to figure out how to integrate this into my bash script. Here is my current attempt:

users=$(cat cutted.bash_users)
ssh_keys=$(cat ssh-keys.txt)

if ssh -l $users -i $ssh_keys $hosts_known -o BatchMode=yes -o 
ConnectTimeout=5
then echo $users:$hosts_known:$ssh_keys SUCCESS >> results.txt
else
echo FAILED
fi

Answer 1

Unfortunately, it seems I cannot add a comment (need 50 reputation points), this is why I am adding my reply to you guys. Also, I've previously edited my question but I received this notification:

Your suggested edit is pending review. Patrick Mevzek reviewed this 2 hours ago: Reject This edit was intended to address the author of the post and makes no sense as an edit. It should have been written as a comment or an answer.

welcome to U&L, you know ssh have a return code ? along with -o BatchMode=yes this can help automatize test. (e.g. if ssh ... ; then echo good for ... >> good.txt ; else echo bad for ... >> bad.txt ; fi) – Archemar 54 mins ago Also that cat|grep|cut|for can be boiled down to for homedir in $(awk -F: '$7 ~ //bin/bash/ { print $6 }' /etc/passwd); do.... – DopeGhoti 1 min ago

So just to clarify: what you are trying to do is, for each user, for every host in their known_hosts, attempt to log into each host with each presumptive private key found in ~username/.ssh? – DopeGhoti 25 mins ago : YES

here;

So now I'm trying to figure out how I could make this idea integrate itself into my bash script, something like;

users=$(cat cutted.bash_users)
cat ssh-keys.txt | awk '{print $9}' > cutted.ssh_keys.txt
ssh_keys=$(cat cutted.ssh_keys.txt)

if ssh -l $users -i $ssh_keys $hosts_known -o BatchMode=yes -o ConnectTimeout=5
then echo $users:$hosts_known:$ssh_keys SUCCESS >> results.txt
else
echo $users:$hosts_known:$ssh_keys FAILED >> not-active.txt
fi

If you guys have an idea on how to make this possible, I would be very happy to learn on how to do it

Thanks