Book Image

Practical Linux Security Cookbook - Second Edition

By : Tajinder Kalsi
Book Image

Practical Linux Security Cookbook - Second Edition

By: Tajinder Kalsi

Overview of this book

Over the last few years, system security has gained a lot of momentum and software professionals are focusing heavily on it. Linux is often treated as a highly secure operating system. However, the reality is that Linux has its share of security ?aws, and these security ?aws allow attackers to get into your system and modify or even destroy your important data. But there’s no need to panic, since there are various mechanisms by which these ?aws can be removed, and this book will help you learn about different types of Linux security to create a more secure Linux system. With a step-by-step recipe approach, the book starts by introducing you to various threats to Linux systems. Then, this book will walk you through customizing the Linux kernel and securing local files. Next, you will move on to managing user authentication both locally and remotely and mitigating network attacks. Later, you will learn about application security and kernel vulnerabilities. You will also learn about patching Bash vulnerability, packet filtering, handling incidents, and monitoring system logs. Finally, you will learn about auditing using system services and performing vulnerability scanning on Linux. By the end of this book, you will be able to secure your Linux systems and create a robust environment.
Table of Contents (20 chapters)
Title Page
Copyright and Credits
Contributors
Packt Upsell
Preface
Index

Blocking incoming traffic


One of the most important tasks for a Linux system administrator is to control access to the network services. At times, it may be better to block all incoming traffic on the server and only allow required services to connect.

Getting ready

As we will be using iptables here as well, no extra packages are needed to perform these steps. We just need a user account with super user access. However, this account should preferably not be a root account.

How to do it...

We will configure Iptables to deny everything, except the traffic that has been initiated from inside our system (for example, the web browsers have web traffic, or some downloading has already been initiated earlier for updating the package or any other software):

  1. As in the previous examples, our first rule in Iptables will be to allow access to localhost data. Run the following command to do this:
iptables -A INPUT -i lo -j ACCEPT 
  1. Our next rule will be for accepting all traffic related to outbound connections...