10 Linux Service Account Best Practices

A service account is a user account that is created specifically for an application or a service. Service accounts are used to provide a security context in which the application or service can run.

In Linux, service accounts are typically created in the /etc/passwd file. The service account is given a unique user ID (UID) and is assigned a home directory, a default shell, and a password.

Service accounts are a necessary part of any Linux system. However, there are a few best practices that should be followed when creating and using service accounts.

1. Use a service account for each application

If an attacker were to compromise an application running as a service account, they would only have access to the resources that particular application needs. This limits the damage that can be done and makes it easier to contain the breach.

If, on the other hand, all applications ran as a single service account, then a breach of any one of those applications would give the attacker access to all of the resources that account has access to. This would greatly increase the scope of the breach and make containment much more difficult.

2. Limit the privileges of service accounts

If a service account is compromised, an attacker can use the same privileges to launch further attacks or escalate their privileges on the system. By limiting the privileges of service accounts, you can reduce the impact of a compromise and make it more difficult for an attacker to move laterally within your environment.

There are several ways to limit the privileges of service accounts, but one of the most effective is to use role-based access control (RBAC). With RBAC, you can assign specific roles to service accounts that define what they can and cannot do. For example, you could create a role that allows a service account to start and stop services, but not modify configuration files.

Linux service accounts are a necessary part of running services, but it’s important to remember that they can also be a security risk. By following best practices, such as limiting privileges and using RBAC, you can minimize the risk and keep your systems secure.

3. Disable password-based logins for service accounts

If an attacker were to gain access to a service account’s password, they could use that account to escalate their privileges and wreak havoc on your systems. By disabling password-based logins for service accounts, you make it much more difficult for an attacker to gain unauthorized access to those accounts.

There are a few different ways to disable password-based logins for service accounts. One way is to use a tool like Ansible to configure your systems. Another way is to manually edit the /etc/shadow file on each system and remove the service account’s password hash.

Whichever method you choose, make sure you test it thoroughly before implementing it in production.

4. Don’t use root as a service account

The root account is the most privileged account on a Linux system. It has full access to all files and can perform any action. As such, it’s a prime target for attackers. If an attacker were to compromise a service running as root, they would effectively have control of the entire system.

Therefore, it’s important to use a separate, unprivileged account for each service. This way, if one service is compromised, the attacker won’t automatically gain access to the rest of the system.

5. Create a separate group for each service account

If multiple services run under the same service account, and that service account is compromised, all of those services are now at risk. By creating a separate group for each service account, you can more easily control access to the various services.

For example, if you have a web server and a database server, each running under its own service account, you can give the web server group access to the database server without giving them access to any other servers. This way, even if the web server is compromised, the attacker would only be able to access the database and not any other servers on the network.

6. Grant access to files and directories with ACLs

When you create a new file or directory, the permissions are set so that only the owner can access it. This is fine for most cases, but there are times when you need to give other users access to the file or directory. For example, if you’re creating a website, you’ll need to give the web server user read and execute permissions to the files in your document root directory.

The easiest way to do this is with ACLs (Access Control Lists). With ACLs, you can add additional users and groups to a file or directory, and specify what permissions they have.

To add an ACL to a file or directory, use the setfacl command. For example, to give the www-data user read and execute permissions to the /var/www/html directory, you would use the following command:

setfacl -m u:www-data:rx /var/www/html

You can also use ACLs to give groups permissions to files and directories. For example, to give the www-data group read and execute permissions to the /var/www/html directory, you would use the following command:

setfacl -m g:www-data:rx /var/www/html

If you want to give all users read and execute permissions to the /var/www/html directory, you can use the “other” permission:

setfacl -m o:rx /var/www/html

ACLs are a powerful tool, and you should use them whenever you need to give users or groups access to files or directories.

7. Monitor file permissions on sensitive data

If an attacker were to gain access to a service account with read permissions on sensitive data, they could potentially exfiltrate this data without being detected. To prevent this from happening, it’s important to monitor file permissions and ensure that only the necessary people have access to sensitive data.

One way to do this is to use a tool like Tripwire to monitor file permissions and send alerts when changes are made. This way, you can quickly detect and investigate any unauthorized changes.

Another way to help mitigate this risk is to encrypt sensitive data. This way, even if an attacker were to gain access to the data, they would not be able to read it without the encryption key.

8. Check for unauthorized changes in your crontab

The crontab is a file that contains instructions for the cron daemon, which is a program that runs specified commands at specified times. The crontab is typically used to automate system maintenance or administration tasks, but it can also be used to run arbitrary commands.

If an attacker gains access to a user’s crontab, they can use it to schedule malicious commands to be executed at a later time. This could allow the attacker to gain a persistent foothold on the system, even if the initial compromise is discovered and remediated.

To prevent this type of attack, you should regularly check the crontab for unauthorized changes. You can do this manually by inspecting the file, or you can use a tool like Tripwire to automatically detect changes.

9. Audit user activity on your Linux systems

User activity auditing helps you track which users are doing what on your systems. This is important for a few reasons.

First, it allows you to see if any unauthorized activity is taking place. If you see a user doing something they shouldn’t be, you can take steps to stop it and prevent any damage that might have been caused.

Second, auditing user activity can help you troubleshoot problems. If you see that a particular user is having difficulty with a certain task, you can investigate and see if there’s anything you can do to help them.

Finally, auditing user activity can help you improve your security posture. By understanding how users are interacting with your systems, you can make changes to improve your security. For example, if you see that users are frequently accessing sensitive data, you might want to consider implementing additional security measures to protect that data.

10. Automate security checks with Tripwire Enterprise

Tripwire Enterprise can help you automate the process of checking for changes to files, directories, and permissions on your Linux systems. This way, you can quickly and easily identify any unauthorized changes that have been made, and take corrective action if necessary.

Additionally, Tripwire Enterprise can help you monitor for compliance with security policies, such as those related to service accounts. By automating these checks, you can ensure that your systems are always in compliance, and reduce the risk of potential security breaches.