OPS235 Lab 7 - Fedora17
- 1 Setup and Configure Secure Shell Services (ssh) Using Virtual Machines
- 1.1 Objectives
- 1.2 Reference
- 1.3 Required materials
- 1.4 Lab Preparation
- 1.5 Lab Investigations
- 1.5.1 Investigation 1: How do you enable the sshd service.
- 1.5.2 Investigation 2: How do you establish an ssh connection.
- 1.5.3 Investigation 3: How do you establish an ssh connection using Public Key Authentication.
- 1.5.4 Investigation 4: How do you use scp and sftp.
- 1.5.5 Investigation 5: How do you use ssh to tunnel X.
- 1.5.6 Investigation 6: How do you use ssh to tunnel other traffic.
- 1.5.7 Investigation 7: How do you make sshd more secure.
- 1.6 Completing the lab
- 1.7 Preparing for the Quizzes
Setup and Configure Secure Shell Services (ssh) Using Virtual Machines
- To set up, configure Secure Shell Services (ssh/sshd)
- To use the ssh, scp, and sftp clients to access another host securely
- Use ssh to tunnel X applications
- Use ssh to tunnel other traffic
- To customize sshd to create a more private, secure system
- IPTables Reference
- man pages for ssh, ssh-keygen, sshd_config, ssh_config, scp, netstat, sftp, ifconfig, ping, arp, netstat, service
- A good ssh tutorial
- A good HOW-TO to make ssh more secure
- Fedora 12 Live CD or a classmate on the same pod
- One SATA hard disk in a removable drive tray with Fedora host and 3 Fedora Virtual Machines installed
- Completion of Lab 6
Investigation 1: How do you enable the sshd service.
- OpenSSH should have been installed by default. Lets confirm this by issuing the command:
rpm -qa | grep ssh
- You should see a number of packages installed including
openssh-server<code> installs a service called <code>sshd<code>, confirm this service is running by issuing the command:
<code>service sshd status
- Now check that the sshd service is configured to start for runlevels 2, 3, 4, & 5, by issuing the command:
chkconfig --list sshd
- If the service is not configured correctly fix it by issuing the command:
chkconfig --level 2345 sshd on
- Now that you know the service is running investigate what port number and protocol sshd uses by issuing the command:
- What protocol and port is the sshd process using?
- What is the state of the port?
- Why do UDP ports not have a state?
- Reissue the
netstatcommand without the
- What is the difference?
noption tells netstat to list everything with numerical values, without it netstat resolves IP addresses and port numbers to host names and protocol names using the files
netstatis a very useful command for anything to do with networking. Read its man page and make sure you understand its output.
- Make sure your
sshdservice is running on all 3 of your VM's
- Answer the Investigation 1 question in your lab log book.
Investigation 2: How do you establish an ssh connection.
- Establish an ssh connection to your fedora3 VM using the command:
- Where 'ops235' is the account on fedora3 and 'fedora3' is the hostname of the fedora3 VM.
- You should receive a message similar to the following:
The authenticity of host 'fedora3 (192.168.235.13)' can't be established. RSA key fingerprint is 53:b4:ad:c8:51:17:99:4b:c9:08:ac:c1:b6:05:71:9b. Are you sure you want to continue connecting (yes/no)? yes Warning: Permanently added 'fedora3' (RSA) to the list of known hosts.
- Answer yes to add to the list of known hosts.
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ WARNING: POSSIBLE DNS SPOOFING DETECTED! @ @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ The RSA host key for fedora3 has changed, and the key for the according IP address 192.168.235.13 is unchanged. This could either mean that DNS SPOOFING is happening or the IP address for the host and its host key have changed at the same time. Offending key for IP in /home/user1/.ssh/known_hosts:10 @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @ @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY! Someone could be eavesdropping on you right now (man-in-the-middle attack)! It is also possible that the RSA host key has just been changed. The fingerprint for the RSA key sent by the remote host is 96:92:62:15:90:ec:40:12:47:08:00:b8:f8:4b:df:5b. Please contact your system administrator. Add correct host key in /home/user1/.ssh/known_hosts to get rid of this message. Offending key in /home/user1/.ssh/known_hosts:53 RSA host key for fedora3 has changed and you have requested strict checking. Host key verification failed.
- When prompted enter your password for your ops235 account on fedora3.
- Establish an ssh connection using your learn account from fedora3 to fedora2.
- Logout of your ssh connection by typing
- Check the state of the connection after logging out. Wait a few minutes and then check again. Record your observations.
- Make certain to exit all connections, and that your shell is located in your Fedora2 server. You can verify this by entering the command:
- Use the Internet to search for "TCP 3 way handshake" to see how TCP connections are established and closed.
- Answer the Investigation 2 question in your lab log book.
Investigation 3: How do you establish an ssh connection using Public Key Authentication.
- Start by generating a keypair as your learn account on fedora2 using the command:
ssh-keygen -t dsa
- That should generate output similar to the following:
Generating public/private dsa key pair. Enter file in which to save the key (/home/user1/.ssh/id_dsa): Enter passphrase (empty for no passphrase): Enter same passphrase again: Your identification has been saved in /home/user1/.ssh/id_dsa. Your public key has been saved in /home/user1/.ssh/id_dsa.pub. The key fingerprint is: 93:58:20:56:72:d7:bd:14:86:9f:42:aa:82:3d:f8:e5 user1@fedora2
- After generating the keys it prompts you for the location to save the keys. The default is
~/.sshYour private key will be saved as
id_dsaand your public key will be saved as
- Once your keys have been saved you should check to make sure the permissions of the
.sshdirectory and your key files are secure.
- Use the following commands to secure them:
chmod 700 ~/.ssh
chmod 600 ~/.ssh/id_dsa*
- The next step is to copy your public key to fedora3 (the remote host). You can use the scp command to do it.
scp(secure copy) is used to copy files between hosts over the ssh protocol. The files are sent over an encrypted channel as is all ssh traffic.
- Issue the command:
scp ~/.ssh/id_dsa.pub ops235@fedora3:
- This will copy your public key to your ops235 home directory on fedora3.
- The : is important as it separates the hostname from the path where it is copied to.
- The default location is the users home directory on the remote host but you can also use an absolute or relative path after the :
- Enter your password to complete the copy.
- Now ssh to fedora3 using a password to authenticate.
- Once logged in to fedora3 we need to add the public key to your list of authorized_keys
- he safest way to do this is to append the contents of
.ssh/authorized_keysfile. To do this use the command:
cat ~/id_dsa.pub >> ~/.ssh/authorized_keys
- Once again you should secure the
.sshdirectory and the
authorized_keysfile using the following commands:
chmod 700 ~/.ssh
chmod 600 ~/.ssh/authorized_keys
- Logout of fedora3 and log back in again.
- You should be prompted to enter your passphrase to unlock your private key.
- Now we can ssh into fedora3 from fedora2 using 2 different authentication methods.
- MaKe certain to logout of your Fedora3 system. Use the
hostnamecommand to verify you are back in your Fedora2 server.
- Answer the Investigation 3 question in your lab log book.
Investigation 4: How do you use scp and sftp.
- To connect to a remote host type the command:
- This will establish an interactive session after authentication.
helpto see the list of sftp commands at any time.
- The 2 main commands are
putto copy a file from the local host to the remote host (upload) and
getto copy a file from the remote host to the local host (download).
- Try using
sftpto transfer files back and forth between hosts.
- As you did previously you can also use the
scpcommand to copy files to and from remote hosts and even from one remote host to another.
scpto copy your services file to the fedora3 host into the /tmp directory. (The path on a remote host follows the :) using the command:
scp /etc/services ops235@fedora3:/tmp
- Experiment with
scpto copy a file from fedora3 directly to fedora1.
- Answer the Investigation 4 question in your lab log book.
Investigation 5: How do you use ssh to tunnel X.
You can also use ssh to tunnel window and bitmap information. Allowing us to login to a remote desktop host and run a Xwindows application such as
firefox and the application will run on the remote host but be displayed on the local host.
- From fedora2
sshto fedora1 using the following command:
ssh -X -C user@fedora1(Where 'user' is your learn account on fedora1). The
-Xenables the forwarding of X window information, and the
-Cenables compression for better performance.
- Once connected run the
geditapplication. (Gnome Text Editor)
- The gedit window will display on fedora2 but it is running fedora1.
- Enter some text and save a file with
- Where was the file saved?
- Experiment with running other GUI applications through
- Answer the Investigation 5 question in your lab log book.
Investigation 6: How do you use ssh to tunnel other traffic.
- You will be working with the 2nd scenario of bypassing a firewall that blocks http traffic.
- In this investigation fedora1 will be your http server and fedora2 will be your client.
- On the HTTP server (fedora1), make sure the Apache web server is installed by typing the command:
rpm -q httpd
- If it is installed check the configuration of the service to see if it is automatically started at any runlevels by issuing the command:
chkconfig --list httpd
- If it has not been started automatically start the service using the command:
service httpd start
- Confirm that httpd is listening to TCP/80 using the command:
- Create a small html document called
/var/www/html/index.htmlthat displays a short message.*
- On the fedora1 (the http server) confirm everything is working locally by using a browser to connect to http://localhost
- The default firewall configuration on fedora1 is to REJECT incoming requests to http (TCP/80)
- Confirm that you can't connect by using firefox on fedora2 to connect to fedora1 http://fedora1/
- On fedora2 confirm that the httpd service is stopped so it cannot interfere with your observations.
- The next step is to establish a tunnel. When you establish a tunnel you make an ssh connection to a remote host and open a new port on the local host. That local host port is then connected to a port on the remote host through the established tunnel. When you send requests to the local port it is forwarded through the tunnel to the remote port.
- Establish a tunnel using a local port on fedora2 of 20808, that connects to the remote port on fedora1 of 80, using the following command on fedora2:
ssh -L 20808:fedora1:80 user@fedora1
- Once the tunnel is established use netstat to verify the port 20808 is listening on fedora2
- Now using the browser on fedora2 connect to http://localhost:20808
- You should see the index.html page on fedora1.
- Close the ssh connection and verify that the port 20808 is no longer listening.
- nswer the Investigation 6 question in your lab log book.
Investigation 7: How do you make sshd more secure.
- Think of a good quality password and change your root passwords on all 3 VM's to be more secure. (It would be a good idea to do this for non-root accounts also)
- The next change you can make is to prevent the root account from logging in to sshd altogether.
- Edit the file
/etc/ssh/sshd_configand look for the option
PermitRootLogin. Uncomment the option (or add the option if it does not appear) and change the option value to
- Even better, it is possible to restrict access to just specific users that require it.
- Edit the file
/etc/ssh/sshd_configand add a new option of
"AllowUsers account"using your login account for account.
- In order for these changes to be effective, issue the following command to restart the sshd service:
service sshd restart
- Now any hacking attempt also has to guess an account name as well as the password. If you need to ssh with root access, ssh as a regular user and use
su -to become root.
- Next change the default port number that sshd uses (TCP:22).
- Edit the sshd configuration file again and change the port number it uses to 2200.
- Restart the service.
- Confirm the new port is being used with a
- Before we can use this new port we must change our firewall to allow traffic through the new port number and block access to port 22:
iptables -I INPUT -p tcp -s0/0 --dport 22 -j DROP
iptables -I INPUT -p tcp -s0/0 --dport 2200 -j ACCEPT
- To test the new port connect to fedora1 from fedora2 using the following command:
ssh -p 2200 user@fedora1
- Finally as a system administrator you should periodically monitor your system logs for unauthorized login attempts.
- On Fedora systems the log file that is used is
- It also logs all uses of the
- Attempt to connect to all of your VM's as root and other users using both public key and password authentication. Use some su and sudo commands also.
- Inspect the log to see what kind of information is logged.
- Answer the Investigation 7 question in your lab log book.
Completing the lab
Arrange proof of the following on the screen:
- have configured sshd to allow connections over a non default port.
- have logged in to a VM using public key authentication
- have scp'd and sftp'd files to a VM.
- have tunneled Xwindows applications through ssh
- have tunneled http through firewall using ssh
- have secured ssh against root access
Preparing for the Quizzes
- What port does sshd use by defaults?
- What file is used to configure sshd?
- What sftp commands are used to upload/download files?
- What kind of files are stored in the "~/.ssh/" directory?
- How do you determine whether the sshd service is running on your system or not?
- What is the purpose of the ~/.ssh/known_hosts file?
- What is the purpose of the ~/.ssh/authorized_keys file?
- Which system log file records each use of the sudo command?
- How do you stop the sshd service?
- How do you tunnel XWindows applications?
- What port is the default scp port?
- What port(s) is/are used by httpd service?