Book Image

Mastering Linux Security and Hardening - Third Edition

By : Donald A. Tevault
3.7 (7)
Book Image

Mastering Linux Security and Hardening - Third Edition

3.7 (7)
By: Donald A. Tevault

Overview of this book

The third edition of Mastering Linux Security and Hardening is an updated, comprehensive introduction to implementing the latest Linux security measures, using the latest versions of Ubuntu and AlmaLinux. In this new edition, you will learn how to set up a practice lab, create user accounts with appropriate privilege levels, protect sensitive data with permissions settings and encryption, and configure a firewall with the newest firewall technologies. You’ll also explore how to use sudo to set up administrative accounts with only the privileges required to do a specific job, and you’ll get a peek at the new sudo features that have been added over the past couple of years. You’ll also see updated information on how to set up a local certificate authority for both Ubuntu and AlmaLinux, as well as how to automate system auditing. Other important skills that you’ll learn include how to automatically harden systems with OpenSCAP, audit systems with auditd, harden the Linux kernel configuration, protect your systems from malware, and perform vulnerability scans of your systems. As a bonus, you’ll see how to use Security Onion to set up an Intrusion Detection System. By the end of this new edition, you will confidently be able to set up a Linux server that will be secure and harder for malicious actors to compromise.
Table of Contents (22 chapters)
1
Section 1: Setting up a Secure Linux System
9
Section 2: Mastering File and Directory Access Control (DAC)
12
Section 3: Advanced System Hardening Techniques
20
Other Books You May Enjoy
21
Index

Using ACLs to access files in the shared directory

As things currently stand, all members of the marketing group have read/write access to all other group members’ files. Restricting access to a file to only specific group members is the same two-step process that we’ve already covered.

Setting the permissions and creating the ACL

First, Vicky sets the normal permissions to only allow herself to have read/write permissions on the file. Then, she’ll create an ACL that will allow Cleopatra to read the file:

[vicky@localhost marketing]$ echo "This file is only for my good friend, Cleopatra." > vicky_file.txt
[vicky@localhost marketing]$ chmod 600 vicky_file.txt
[vicky@localhost marketing]$ setfacl -m u:cleopatra:r vicky_file.txt
[vicky@localhost marketing]$ ls -l
total 4
-rw-rw-r--. 1 charlie marketing 0 Nov 13 15:59 charlie_file.txt
-rw-r-----+ 1 vicky marketing 49 Nov 13 16:24 vicky_file.txt
[vicky@localhost marketing]$ getfacl vicky_file...