Category Archives: How To

How to Restrict Internet Access to a Single Program on Arch Linux with Firejail

Sometimes, we may need to restrict the internet access to a single application both for security reasons or testing purposes.

On Linux, there are different ways to restrict the internet access to a single program. Unfortunately, most of them, are not straightforward at all.

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How to Sandbox Non-trusted Apps in Linux Systems

Sometimes we have to run an application that we do not trust, but we are afraid that it might look at or delete our personal data, since even though Linux systems are less prone to malware, they are not completely immune. Maybe you want to access a shady-sounding website. Or perhaps you need to access your bank account, or any other site dealing with sensitive private information. You might trust the website, but do not trust the add-ons or extensions installed in your browser.

In each of the above cases, sandboxing is useful. The idea is to restrict the non-trusted application in an isolated container -a sandbox– so that it does not have access to our personal data, or the other applications on our system. While there is a software called Sandboxie that does what we need, it is only available for Microsoft Windows. But Linux users need not worry, since we have Firejail for the job.

So without further ado, let us see how to set up Firejail on a Linux system and use it to sandbox apps in Linux:

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Jailing the Zoom Client

While there are many Open Source solutions for browser-based videoconferencing and online meetings, like BigBlueButton or Jitsi, I am still forced to use zoom in a lot of contexts.

But the zoom web client lacks a lot of functionality and generally does not work well in my experience.

On the other hand I absolutely distrust the zoom client. Just inspect the strings that appear in the binary of the launcher…

$ strings /opt/zoom/ZoomLauncher | grep grep
pacmd list-sinks |grep 'name:\|module:'

Yes, they are using a lot of shell commands in their compiled binaries. Firejail to the rescue!

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Advanced Browser Security with Firejail – A Hands On Guide

Many people believe that browser security is difficult. I created this guide as an overview of Firejail sandboxing technology. The goal is to show you that security can be simple and fun.

The video guide is structured as a hacking session. The victim is running a sandboxed browser. An imaginary zero-day exploit gives the attacker control of the sandbox in the form of a remote shell. Let’s see what damage we can do. And maybe, reconfigure the sandbox so the victim can survive the aftermath of such an attack.

Enjoy!

Restricting Programs From Backdoors/IP Leaks (Audacity Example)

Video on Odysee

Take a look at your Desktop and/or interface. Be it MATE (desktop/laptop), Phosh (Pinephone/Librem), or KDE. We use several buttons/shortcuts to programs everyday. Some of these need the internet. Some do not.

Have you minimized access to programs who do not need the internet? Did you know some programs secretly “call home” and share data/your IP address with 3rd parties (sometimes sold)? The most ideal setup is one which is restricted wherever possible, but not up to the point where your setup becomes unusable.

Here we are going to use a Hot Off the Press News example to demonstrate how to allow networking only to those programs requiring it (such as web browsers, encrypted messengers, etc). Other programs like VLC Media player, GIMP (image manipulation), and Libre Office do NOT need ANY networking for full functionality. So why do we allow it? Because this is default behavior, we accept it. We are going to change that today.

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Firejail on Linux to sandbox all the things

Firejail is a program that can prepare sandboxes to run other programs. This is an efficient way to keep a software isolated from the rest of the system without need of changing its source code, it works for network, graphical or daemons programs.

You may want to sandbox programs you run in order to protect your system for any issue that could happen within the program (security breach, code mistake, unknown errors), like Steam once had a “rm -fr /” issue, using a sandbox that would have partially saved a part of the user directory. Web browsers are major tools nowadays and yet they have access to the whole system and have many security issues discovered and exploited in the wild, running it in a sandbox can reduce the data a hacker could exfiltrate from the computer. Of course, sandboxing comes with an usability tradeoff because if you only allow access to the ~/Downloads/ directory, you need to put files in this directory if you want to upload them, and you can only download files into this directory and then move them later where you really want to keep your files.

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Securely Run Programs In Linux Mint Using Firetools

For running applications sandboxed in Linux, Firetools is a good utility to do so. Sandboxing is essentially restricting applications in their own space and thereby limiting their reach to the overall system. This is a security layer to prevent any malicious programs to have full access to the system.

Firetools is a graphical front-end for the command-line sandboxing tool Firejail.

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