Understanding reverse shells

Shell Game

Article from Issue 275/2023

Firewalls block shell access from outside the network. But what if the shell is launched from the inside?

Recently, I've thoroughly enjoyed brushing up my offensive security skills. I've worked in the defensive security field for longer than I care to remember, and gaining more insight into how attackers perceive the world has really opened my eyes. My background is two-and-half decades of Linux and securing containers over the last seven years or so. An area that always piques my interest is Linux-based local privilege escalation. Once you have found a way of gaining access to a machine, the Holy Grail is elevating your privileges to the root user so you have full control.

Sometimes achieving root can take a little time. As an attacker, it is important to be able to return at a later date if you haven't achieved root user privileges yet or you want to monitor changeable data on a machine. Penetration testers and attackers would call this ongoing access persistence, which is the ability to gain a foothold and then maintain access; you might also call it creating a backdoor.

Attackers have a multitude of ways for ensuring that, if a machine reboots or some other event occurs, a backdoor is re-established automatically. This article looks at reverse shells and provides some examples of how to achieve persistence once you have gained access to a Linux machine. It should go without saying that you should use the following information for testing, practicing, and improving your knowledge and not for some nefarious purpose.


Use Express-Checkout link below to read the full article (PDF).

Buy this article as PDF

Express-Checkout as PDF
Price $2.95
(incl. VAT)

Buy Linux Magazine

Get it on Google Play

US / Canada

Get it on Google Play

UK / Australia

Related content

  • Compromising WordPress

    WordPress is an incredibly popular tool for building websites, and don't think the attackers haven't noticed. We'll show you what to watch for.

  • Local File Inclusion

    A local file inclusion attack uses files that are already on the target system.

  • Privilege Escalation

    Even a small configuration error or oversight can create an opening for privilege escalation. These real-world escalation techniques will help you understand what to watch for.

  • Backdoors

    Backdoors give attackers unrestricted access to a zombie system. If you plan to stop the bad guys from settling in, you’ll be interested in this analysis of the tools they might use for building a private entrance.

  • PowerShell in Linux

    Microsoft released its PowerShell under a free license in August 2016 and ported the tool to Linux and Mac OS. Is PowerShell for Linux a mere marketing ploy or a real contender that can compete with native Linux shells?

comments powered by Disqus
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters

Support Our Work

Linux Magazine content is made possible with support from readers like you. Please consider contributing when you’ve found an article to be beneficial.

Learn More