Posts tagged login
SSH Login Timeout – Password Authentication
Feb 6th
SSH login timeouts are not very effective at preventing unauthorized login attempts. Most ssh attacks are scripted attached launched by automatic mechanisms. The scripts most likely will use dictionary based brute force attacks that insert the password very quickly. Setting the login timeout very low will most likely not prevent such scripted attacks, and will only hinder the ability for a legitimate user to login successfully within the allocated amount of time. Set the login timeout to 60 seconds; I have set it to 5 seconds and it only caused problems for actual user logins.
Sshd_config Settings Rundown
Feb 3rd
- Image via Wikipedia
First change the port you are using. Do not use port 22 on servers that have internet connectivity. This is the first port that will be checked by countless robots searching the internet for vulnerabilities. Change the port to whatever, and then use the -p option in your ssh login attemt. Then make sure root login is disabled, remove the pound symbol from the front of the option line. If you can you should definitely allow rsa key login. Once you get your encryption key setup disable password login by setting the respective line to “no”. If you cannot enable keyed logins for any reason what soever, you should enabled ip based restrictions either by iptables or by tcp wrappers. Iptables is configured with the iptables command, and the tcp wrappers are configured in /etc/hosts.allow. You can reduce the time limit for password login, but sometimes this causes problems with remote users connecting; sometimes it takes a couple of extra seconds for people to login. Make the time limit around 30 seconds. If people are still having trouble connecting check the /var/log/auth.log file for more information about the failed login attempt. Maybe the password is too complicated? Before reducing the complexity of the password implement fail2ban, which will automatically block ip addresses based on failed login attempts, therefore you can reduce the complexity of the password without substantially reducing system security.
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Detecting a Security Breach – Ubuntu and Linux Machine
Jan 25th
Detecting a security breech is sometimes as easy as logging into the machine, using ssh, and viewing the last login attempt from a completely unrecognized ip address or domain. Subsequently check your auth.log file, in /var/log, for login attempts. If you see countless failed login attempts you have been the victim of a brute from attack. In gedit, or nano you can search for “attempt” or “access”. When several failed login attempts occur a log entry saying “possible breaking attempt” is posted. The first think a hacker will do, on a Linux machine, is attempt to change the root password, which will lock down the machine completely. If they cannot change the root password, they may just try and install a backdoor to the particular user that was breached. A backdoor can be a daemon running on any port, so check with “ps aux | grep user”. Grepping the ps command will bring up all of your active processes and if any process name looks funny you have identified a concern. You can also check what ports are accepting communication (open). A backdoor can also be an installed authorized key, which will allow password-less ssh access to the system.
Ultimately if a hacker changes the root password of your machine, there is nothing you can do. You must either restore from a backup, or rebuild the entire machine. No questions asked.
Server Security – Passwordless Remote Login
Jan 24th
Based on some recent experience do not ever allow password remote login. There are two things you chould apply to your ssh server. Implement a RSA key login, and implement fail2ban. Fail2ban will modify iptables (firewall) to block the ip address of offending attempts to connect. It will do so for your apache, ssh, ftp, and other servers. It is a separate program, not a wrapper, and it monitors log files for login attempts. You set the max login attempts (fails) in the jail.conf file in /etc/fail2ban. The combination of RSA keys and fail2ban will ensure a secure and accessible system, which is a must of the system is to be open to outside internet connections.
Secure Remote Connections – Tech Support
Jan 23rd
If you are going to be providing technical support, to be professional you should implemented a secure ssh connection. There is no excuse to potentially give terminal access to a password snooper. Using ssh the terminal commands themselves are encrypted, so disabling password login truly minimized risks of a security breach. Using a RSA key passwords are not transmitted and the login process is truly encrypted. Disabled password login by changing its option to “no” in the sshd configuration file. The config file is located in /etc/ssh/sshd_config. The default authorized key file is located in the users home directory. ~/.ssh/authorized_keys2. You need to place the id_rsa.pub information in the authorized_keys2 file. You can open the file manually or your can cat it in. You can also replace the entire authorized_keys2 file with id_rsa.pub; but maybe you want multiple authorized keys so use cat or editing manually may be better.
Create a new RSA key with:
ssh-keygen
It will put the new id_rsa and id_rsa.pub in ~/.ssh. When logging in as a client the default location for the id_rsa is in ~/.ssh, but you can place it anywhere using the ssh -i option. Then include the path to the id_rsa key. An example is:
ssh -i /home/user/Desktop/id_rsa user@host
Debain Etch Sudoers File
Aug 17th
Debian is the root of many Linux distibutions. It is extremely clean, and it great for moderate to advanced Linuxed users. To start with a clean Debain install your going to have to add your user name, to the sudoers file, in order to have expected sudo passwordless superuser access. First to open the sudoers file you will have to login as root: use su Type your root password and login. Then open the sudoers file:
nano /etc/sudoers
Simply add at the top of the file:
User_Alias FULLTIMERS = yourusername
yourusername ALL = NOPASSWD: ALL
Then close the file with control o, control x, exit Now you can run superuser (sudo) command without having to enter a password.