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

Remote service login – Telnet


Telnet is one the earliest remote login protocols still in use. It is older than most of the system administrators today, as it was developed in 1969. Telnet allows users to make text-based connections between computers. Since Telnet provides no built-in security measures, it suffers from various security issues.

Getting ready

To demonstrate the use of Telnet, we will use two systems. On the first system, a Telnet server will be running, and from the second system, we will check the security issues.

How to do it...

In this section, we will see how Telnet can cause serious security issues:

  1. Using Telnet is very easy. Just open a terminal window and type the following command:
telnet <IP Address> <Port>

Here is an example: telnet 192.168.43.100 23

  1. When Telnet is running on a server, it can be used by attackers to perform the banner grabbing of other services. Let's use it to find the version of SSH running on the server. Type the following command to do this...