Welcome to the Linux Security Series! In this series, I will tackle the fundamentals of Linux security and how attackers attack Linux machines.

Before we dive into Linux systems security, it’s essential to understand the permissions model of Linux machines. Understanding how to manage permissions on Linux systems will help you understand attacks that exploit the permissions system, like most privilege escalation techniques. Let’s get started.

Linux File Permissions

Linux inherited the Unix model of file ownership and permissions. Every file and folder on the system has a set of permissions that specifies who is allowed to do what with that particular file.

There are three types of permissions: read, write, and execute. A read permission on a file enables a user to read the contents of the file. A _write _permission allows a user to modify or delete the file. And an _execute _permission allows a user to run the file as a script or an executable.

You can view the permissions of a file or directory by using the ls -l command in a directory. You should see a line like this.

-rwxrwxrwx
drwxrwxrwx

The first character indicates whether the item is a file or a directory. A dash means that the item is a file, whereas a d means it’s a directory. The next three characters are the permissions of the file’s owner. The owner is usually the user who created the file and has the most control over it. R indicates read, w indicates write, and X indicates eXecute. And a dash indicates the lack of that permission. Let’s look at an example. Here, the owner can read, write, and execute the file.

-rwxr--r--

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