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

Setting the SGID bit and the sticky bit on the shared directory

I’ve told you before that it’s a bit of a security risk to set either the SUID or SGID permissions on files, especially on executable files. But it is both completely safe and very useful to set SGID on a shared directory.

SGID behavior on a directory is completely different from SGID behavior on a file. On a directory, SGID will cause any files that anybody creates to be associated with the same group with which the directory is associated.

So, bearing in mind that the SGID permission value is 2000, let’s set SGID on our marketing directory:

[donnie@localhost /]$ sudo chmod 2770 marketing
[sudo] password for donnie:
[donnie@localhost /]$ ls -ld marketing
drwxrws---. 2 nobody marketing 28 Nov 13 15:41 marketing
[donnie@localhost /]$

The s in the executable position for the group indicates that the command was successful. Let’s now let Vicky log back in to create another file...