What is AppArmor

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Why Use AppArmor

Installing and Enabling AppArmor on Ubuntu VPS

AppArmor is included by default in Ubuntu. However, it may need to be enabled or updated on your VPS, especially if it has been disabled or if you want to ensure the latest version is running.

To check whether AppArmor is installed and running on your VPS, use the following command:

If AppArmor is running, you will see a status message indicating that it is enabled. If not, proceed with the following steps to install and enable it.

If AppArmor is not installed, you can install it using the following command:

This installs AppArmor and a set of utilities that help manage profiles.

If AppArmor is installed but not running, you can enable it with:

Then, verify that it is running:

Ensure that AppArmor is enabled during the boot process. Open the GRUB configuration file to confirm:

Look for the line that starts with GRUB_CMDLINE_LINUX_DEFAULT. If AppArmor isn’t already enabled, ensure that the line contains apparmor=1 security=apparmor like this:

Save and exit the file, then update GRUB:

Managing AppArmor Profiles

AppArmor works by enforcing security profiles for individual applications. Ubuntu comes with several pre-configured profiles, but you can create, modify, or manage profiles according to your needs.

You can list the existing profiles on your system using:

This will display all enforced and complain-mode profiles on your system.

If you want to switch a profile from enforce to complain mode, use the following command:

To switch it back to enforce mode:

Let’s create a custom profile for the nginx web server as an example.

1- Generate a Profile Template:

AppArmor provides a tool called aa-genprof that allows you to generate profiles interactively. First, stop the nginx service:

Now, use aa-genprof to create a profile for nginx:

The tool will guide you through the process. Start nginx while AppArmor is in learning mode to capture its behavior:

2- Review and Update the Profile:

You will be prompted to review the captured logs and decide whether to allow or deny specific actions. Once the profile is created, you can enforce it:

You can manually edit an AppArmor profile by opening its configuration file. Profiles are stored in /etc/apparmor.d/. For example, to modify the nginx profile:

Edit the profile to add or remove restrictions. After saving your changes, reload the profile with:

Example: Using AppArmor to Secure Nginx

Let’s walk through a practical example of how to use AppArmor to secure nginx on your VPS.

As described above, use aa-genprof to create a profile for nginx, then place it in enforce mode.

Once nginx is running with an enforced profile, try accessing the web server and perform routine operations. AppArmor will ensure that nginx only has access to the files and directories specified in its profile. You can review the logs for any denied operations:

If necessary, you can modify the nginx profile based on the logs and adjust the permissions.

Disabling AppArmor for a Specific Application

If you want to disable AppArmor for a specific application, you can set its profile to unconfined:

This will stop AppArmor from enforcing any restrictions on the application.

AppArmor is a powerful security tool that enhances the security of your Ubuntu VPS by limiting what applications can do on your system. By creating and enforcing application-specific profiles, you can significantly reduce the risk posed by compromised software. With this guide, you’ve learned how to install and configure AppArmor, create custom profiles, and secure applications like nginx. By regularly managing and updating these profiles, you can keep your VPS more secure and resistant to attacks.