Editing File Permissions in Linux

Project Overview

In this project, I demonstrated how to manage and update file permissions in a Linux environment. File permissions are a critical aspect of system security, determining who can read, write, or execute files on a Linux system.

The goal was to properly configure permissions to ensure that only authorized users could access or modify sensitive files, a fundamental principle of cybersecurity.

Scenario

As a security professional, I was tasked with updating file permissions for a set of sensitive files on a Linux server. The permissions needed to be configured according to the principle of least privilege, ensuring that:

• Regular users could only access files they needed for their work
• System administrators had appropriate access
• Some files were protected from modification by any user

Implementation

The following commands were used to check and modify file permissions:

Checking Current Permissions

First, I checked the current permissions of the files:

jacob@Jacobs-PC:~ $ ls -l /home/data/
-rw-rw-r-- 1 admin staff 8425 Apr 1 08:30 financial_report.txt
-rwx------ 1 admin admin 2048 Apr 1 08:30 system_backup.sh
-rw-r--r-- 1 admin staff 1650 Apr 1 08:30 user_list.txt

Understanding Permission Notation

Linux file permissions are represented by a string of characters:

• First character: File type (- for regular file, d for directory)
• Next three characters: Owner permissions (r=read, w=write, x=execute)
• Next three characters: Group permissions
• Last three characters: Others permissions

Modifying Permissions

I applied the following changes:

• Restricted access to the financial report so only the owner can write to it
• Ensured system administrators can execute the backup script
• Made the user list readable but not writeable by regular users

Using chmod Command

The chmod command is used to change file permissions. I used it with both symbolic and numeric notation:

jacob@Jacobs-PC:~ $ chmod u=rw,g=r,o=r /home/data/financial_report.txt
jacob@Jacobs-PC:~ $ chmod 750 /home/data/system_backup.sh
jacob@Jacobs-PC:~ $ chmod 444 /home/data/user_list.txt

Changing Ownership

I also needed to change ownership of some files using the chown command:

jacob@Jacobs-PC:~ $ sudo chown admin:sysadmin /home/data/system_backup.sh

Verifying Changes

After making all changes, I verified the new permissions:

jacob@Jacobs-PC:~ $ ls -l /home/data/
-rw-r--r-- 1 admin staff    8425 Apr 1 08:30 financial_report.txt
-rwxr-x--- 1 admin sysadmin 2048 Apr 1 08:30 system_backup.sh
-r--r--r-- 1 admin staff    1650 Apr 1 08:30 user_list.txt

Security Implications

By implementing these permission changes, I achieved the following security benefits:

1. Least Privilege: Users only have access to what they need for their jobs
2. Data Protection: Sensitive financial data can only be modified by authorized users
3. System Security: System scripts can only be executed by administrators
4. Information Control: Crucial information is available for reference but protected from unauthorized changes

This implementation demonstrates the importance of proper file permissions in maintaining a secure Linux environment. By understanding and correctly applying file permission concepts, organizations can significantly reduce their attack surface and protect sensitive data from unauthorized access or modification.

Best Practices for Linux File Permissions

Based on this project, I recommend the following best practices:

• Regularly audit file permissions to ensure they remain appropriate
• Use group permissions effectively to manage access for different teams
• Remove write access from files that should not be modified
• Restrict execute permissions to only necessary files and users
• Consider using Access Control Lists (ACLs) for more granular control when needed