fatal: [matrix2.host.com]: UNREACHABLE! => changed=false

Error while attempting to run playbook
ansible-playbook -i inventory/hosts setup.yml --tags=setup-system-user --ask-become-pass

Looks like the above issue is that Ansible is not able to authenticate with the server. By default it looks to try and use ssh keys, but I don’t have any passwordless ssh keys set up for Ansible to use so it fails while attempting to connect. The work around it to make sure you have sshpass installed and then specify –ask-pass to the end of the command.

ansible-playbook -i inventory/hosts setup.yml --tags=setup-system-user --ask-become-pass --ask-pass

When the command runs it’ll ask you for the ssh password and then use that.

Unable to Remove Authorized SSH Keys from AirOS

For some reason I ran into an issue where I can not remove authorized SSH Keys in AirOS version 6.3. It redirects to a 404 page and then to the main page.

Attempting to remove SSH keys in AirOS
404 Error while attempting to remove SSH keys

Thankfully, we can still remove the authorized keys from the command line. For more information on making changes over SSH, refer to the following post.

SSH into radio. Replace username and IP address with your radios user and IP.

ssh ubnt@192.168.1.20

Open up config file

vi /tmp/system.cfg

Search for the lines that contain

the sshd.auth.key and remove them

Remove the sshd.auth.key lines

Save the file and write the configuration with

/usr/etc/rc.d/rc.softrestart save

Once the command completes, you should be good to go.

Configure UFW Firewall on Ubuntu

UFW Firewall Status

Below are some simple commands around working with UFW. UFW is included in Ubuntu. However it may need to be enable.

Show status

sudo ufw status

Disable UFW Service

sudo systemctl stop ufw && sudo systemctl disable ufw

Stop UFW Service

sudo systemctl stop ufw

Start UFW service

sudo systemctl stop ufw

Enable UFW

sudo ufw enable

Allow SSH

sudo ufw allow 22/tcp

Show status

sudo ufw status numbered

Example output

sudo ufw status numbered
Status: active
To            Action   From 
--            ------   ----
[1] 3478/udp  ALLOW IN  Anywhere
[2] 5514/udp  ALLOW IN  Anywhere
[3] 8080/tcp  ALLOW IN  Anywhere
[4] 8443/tcp  ALLOW IN  Anywhere
[5] 8880/tcp  ALLOW IN  Anywhere
[6] 8843/tcp  ALLOW IN  Anywhere
[7] 6789/tcp  ALLOW IN  Anywhere
[8] 27117/tcp ALLOW IN  Anywhere
[9] 22/tcp    ALLOW IN  Anywhere

Delete rule

You need to know the number of the rule you want to delete. Replace number with the number of the rule from the status command

sudo ufw delete number

Reset rules

sudo ufw reset

Allow access to port from specific IP address

Example command allows access to SSH (port 22) from the 172.16.0.0/12 ip range.

sudo ufw allow proto tcp from 172.16.0.0/12 to any port 22

One note: It appears that you need to run the rule with every IP range you want to allow.

The following link has more information regarding UFW firewall and subnets.
https://www.cyberciti.biz/faq/ufw-allow-incoming-ssh-connections-from-a-specific-ip-address-subnet-on-ubuntu-debian/

How To Increase Session Timeout for SSH

From the server side, edit the /etc/ssh/sshd_config

Change, uncomment, or add

ClientAliveInterval 120
ClientAliveCountMax 15

Change the AliveInterval and CountMax as desired.

More info on the AliveIntercal and CountMax.

ClientAliveCountMax Sets the number of client alive messages which may be sent without sshd(8) receiving any messages back from the client. If this threshold is reached while client alive messages are being sent, sshd will disconnect the client, terminating the session. It is important to note that the use of client alive messages is very different from TCPKeepAlive. The client alive messages are sent through the encrypted channel and therefore will not be spoofable. The TCP keepalive option enabled by TCPKeepAlive is spoofable. The client alive mechanism is valuable when the client or server depend on knowing when a connection has become unresponsive.

The default value is 3. If ClientAliveInterval is set to 15, and ClientAliveCountMax is left at the default, unresponsive SSH clients will be disconnected after approximately 45 seconds. Setting a zero

ClientAliveCountMax disables connection termination.ClientAliveInterval Sets a timeout interval in seconds after which if no data has been received from the client, sshd(8) will send a message through the encrypted channel to request a response from the client. The default is 0, indicating that these messages will not be sent to the client.

More information
https://man.openbsd.org/sshd_config

Hydra – Socket error: Connection reset by peer

[VERBOSE] Disabled child 2 because of too many errors
[VERBOSE] Disabled child 6 because of too many errors
[ERROR] could not connect to target port 22: Socket error: Connection reset by peer
[ERROR] could not connect to target port 22: Socket error: Connection reset by peer
[ERROR] could not connect to target port 22: Socket error: Connection reset by peer
[ERROR] could not connect to target port 22: Socket error: Connection reset by peer
[ERROR] ssh protocol error

Looks like the issue can happen if you have too many threads going at once. Lower the amount of threads your using with -t. Recommended amount for ssh is 4.

hydra -L usernames.txt  -P "passwords.txt" 192.168.1.20 ssh -t4

no matching cipher found. Their offer: aes128-cbc,3des-cbc…

When trying to SSH to older devices like a Ubiquiti Bullet2, you may receive an error saying.

no matching cipher found. Their offer: aes128-cbc,3des-cbc,aes256-cbc,twofish256-cbc,twofish-cbc,twofish128-cbc,blowfish-cbc

Work around it to manually specify the cipher with the “-c” option. You will also probably need to specify the KexAlgorithm

ssh -c aes128-cbc -oKexAlgorithms=+diffie-hellman-group1-sha1 admin@192.168.1.20

You can see what ciphers ssh supports by running “ssh -Q cipher”

Example output

ssh -Q cipher
3des-cbc
aes128-cbc
aes192-cbc
aes256-cbc
rijndael-cbc@lysator.liu.se
aes128-ctr
aes192-ctr
aes256-ctr
aes128-gcm@openssh.com
aes256-gcm@openssh.com
chacha20-poly1305@openssh.com

More information
https://www.openssh.com/legacy.html

Change Channel Width on Ubiquiti AC CPE Over SSH

SSH into CPE

ssh ubnt@192.168.1.20

open up the “/tmp/system.cfg” file

vi /tmp/system.cfg

Find the “radio.1.chanbw=” line and change to the following

radio.1.chanbw=10

Note: it may say “radio.1.chanbw=0” that looks to be the default and works for 20mhz

exit file with

esc + :wq + Return or Enter

Save settings with

/usr/etc/rc.d/rc.softrestart save 

Change AP to 10Mhz and the CPE should reconnect.

no matching key exchange method found. Their offer: diffie-hellman-group1-sha1

Work around is to use the -o option and specify KexAlgorithms with the correcct option.

ssh -o KexAlgorithms=+diffie-hellman-group1-sha1 admin@192.168.11.1

https://unix.stackexchange.com/questions/340844/how-to-enable-diffie-hellman-group1-sha1-key-exchange-on-debian-8-0#340853

no matching host key type found. Their offer: ssh-dss

Reason for it not working is some of the older weaker SSH encryption algorithms have been disabled. You can allow ssh to use it by specifying the following option.

 -oHostKeyAlgorithms=+ssh-dss 

so whole command would look like

ssh  -o HostKeyAlgorithms=+ssh-dss root@192.168.111.4 

http://www.openssh.com/legacy.html

https://askubuntu.com/questions/836048/ssh-returns-no-matching-host-key-type-found-their-offer-ssh-dss#836064