Basic Ubuntu Security Guide, Desktop Edition

Who Did We Write This For?

Security is a very broad, potentially daunting subject to a new Ubuntu user. It's crazy to think that anyone can boil security down to a list of 7 things. So we didn't even try. Instead, our goal is to present a listing of the most basic security concepts that can be fairly easily implemented while you learn. This guide was inspired and written by several new users of Ubuntu who were very interested in learning how to hack around their brand new Ubuntu operating systems. We were lucky enough to have some security professionals collaborate with us. But we still don't claim that we will reduce your risk to zero. We are presenting a pragmatic approach to security.



This guide is intended for the typical, average home user that is in the process of learning how to use Ubuntu. So if you just surf the net, play games (on-line & off-line), do on-line banking, education...then you are the intended audience. However if you are running a network server (especially one that is accessed via the Internet) or if you use Ubuntu in your corporate environment (or simply work from home) then the advice you need is more specialized and beyond the scope of this guide. If you don't know whether you are running a server or not, then read this.





The most basic set of rules

If you're a simple desktop user who only uses his computer for the most ordinary things, then this is the basic rule set:

1. immediately install security updates when you're notified;

2. do not install antivirus, as you *really* don't need it in Linux;unless you share files with Windows

3. enable the firewall (sudo ufw enable) without further tweaks;

4. stick to the official repo's as much as possible, and only deviate from them when strictly necessary and with much caution;

5. keep Java (both openJDK and Oracle Java) disabled by default in your browser, and only enable it when needed;

6. use Wine with caution;

7. and most important of all: use your common sense. The biggest security threat is generally found between keyboard and chair.



If you have higher security needs, then read on.

In order to simplify the very complex world of security, we have broken it down into two sections. In this first section, we will discuss security tools in Ubuntu that you can configure and (once configured) require little interaction. We will also discuss general security concepts that are easy to implement into your daily computer use. There is a lot of existing security information already in existence in the Ubuntu Wikis and stickies in the Ubuntu Forums. There are some great resources there, in fact one of the best guides is linked here. But a lot of that material will seem complex to the new Ubuntu user - so the goal of this guide was to take the existing material and simplify it, making it possible to bridge the gap.





Your Tolerance for Risk

We've all heard the argument that if you make a system secure, you also hinder access, create obstacles, and complicate use. It is up to the individual user to determine what his tolerance for risk is. This Wiki will outline vectors of potential vulnerabilities in your Ubuntu system, and you can evaluate them and determine how those risks relate to your personal situation.





Linux Vulnerabilities

The majority of new users are coming from Windows environments, where security focuses mostly on anti-virus software. To understand security on Ubuntu, you must shift your thinking from this point of view. In the following bullets, we're going to analyze what threats actually effect you as a Ubuntu user.

Myth : If I install an anti-virus program I'll be fine.



Reality : At the time of writing, there are no known viruses on the big bad web designed to target Linux. A few targeting Windows can execute in a manner that could allow compromise of a Linux system via an interpreter layer like Wine. Very few people recommend existing anti-virus software for Linux machines, in part because there are few decent free anti-malware solutions available. Enterprise class solutions are good, but the consumer-grade products aren't on par with their Windows counterparts enough to warrant their use. Moreover, if you focus entirely on viruses then you are ignoring the vast majority of real threats to your Ubuntu machine.



Myth : Security through obscurity keeps me safe.



Reality : It's a favoured argument from Linux supporters, but Linux/Ubuntu is not that obscure to “crackers”. They may be obscure to you or your friends, however, there are many who know how to exploit Linux vulnerabilities just as easy as Windows, Mac OSX, Solaris, AIX, or any other operating system's vulnerabilities. The best defence is knowledge and preparation. Relying on an “obscure” operating system to hide behind is NOT a good strategy.



Myth : I can browse however I want to because malware on the web is mostly designed for Windows.



Reality : While the majority of malware does target Windows, this statement overlooks the fact that an entire spectrum of web based attack vectors exist that work on any operating system. Cross Site Scripting, Cross Site Request Forgery, Click-Jacking, Session Riding, and many other methods can be used to exploit weaknesses in a relationship of trust between you and a website, or a website and you, regardless of your operating system. For things like this we have browser add-ons which will be discussed in the browser security section.



Myth : I don't need to use fancy browser add-ons when using public access wifi because I use Ubuntu.



Reality : An absurd statement. Most attacks carried out on public wifi include several varieties of man in the middle attacks. If you want to utilize public wifi, it is highly discouraged to do anything more than trivial in nature with it unless you are an advanced user and you know how to set up a virtual private network (VPN), a VPN via Secure Shell (SSH), or use Secure Sockets Layer (SSL) in conjunction with SSLstrip.



Myth : I don't need a firewall because Ubuntu has no open ports by default.



Reality : This is a matter of risk tolerance. Added protection, particularly that which takes only a few minutes to set up, is always worth it. Firewalls are discussed in more depth later in this document.



Myth : Windows malware can not compromise Ubuntu.



Reality : Ubuntu CAN be compromised by Windows malware if you're using Wine. This is not to say that Windows malware can infect a Linux system directly, however it CAN, if targeted properly, utilize the Wine interpreter to send system calls to the Linux kernel. This is a very rare case, and it is highly unlikely that it would occur as it would be a very targeted attack. But for completeness sake we should mention that it CAN happen.



Myth : Ubuntu is harder to exploit than Windows, Mac OSX, whatever else - and it's targeted less than those other operating systems as well.



Reality: The process of discovering a vulnerability and exploiting it is pretty much the same across the board, regardless of operating system.



These are just some common myths associated with Ubuntu and security. This list is not comprehensive, but it covers the largest misconceptions held by new users. This does not mean that Ubuntu is inherently insecure, or is less secure than previous versions, or is more/less secure than any other operating system. It is just an effort to dispel common myths and get the reader (you) thinking in a positive direction toward improving their system's security posture. If you follow the steps in this Wiki, you will have a decent defense built to protect your machine from viruses as well as the other more pressing threats out there.



And of course, we'd be remiss not to mention social engineering. What information you're putting into public view? Do you know who you're giving valuable information to? Social engineering is important to understand but beyond the scope of this Wiki.



Backups

Reinstalling an operating system again after it corrupts is annoying. But losing valuable personal pictures, letters, emails... these are priceless and cannot be replaced. If you are prepared to wipe and reinstall with very little notice, then you are far more secure. Moreover, there are many threads in the Ubuntu Forums that describe problems that would have been avoided if the user had made good backups. It is important to make special backups before certain risky operations like upgrading to a new version, operations on partitions and partition tables, using dd, etc. Finally, if you're concerned that your computer has been infected or "cracked," then you can restore Ubuntu to a known previously good state.



To quote the introduction of Duplicity Backup, "There are many different applications that are available to backup Ubuntu. Each one has its strengths and weaknesses. Some are made for enterprise environments where it is necessary to back up many computers quickly and efficiently. Others are made for home environments and come with a simple wizard-driven GUI or command line interface...Each application can backup to one or many DVDs, CDs, disk drives, and other media or may not backup to one or more of those things. As varied as these programs are, so are the needs of the individuals who use them." This link can help you decide where to backup your data, what to backup, and when.





It All Starts With a Good Password

Obviously if an attacker doesn't have your password, then it's harder for him to make changes on your machine. A strong unique password for each account is best - consider using a password safe (but remember that that password MUST be a good one!) Read this discussion regarding the process of choosing a good password.





Know What Sudo is Doing

If you're following a set of instructions and you're about to type in sudo, ask yourself "Do I REALLY know what this command is about to do?" If you can't explain it to your grandmother, then you don't know what's going to happen. Related to that - if you get asked for your password, make sure you know what you've just done to trigger that response. The system is trying to protect you. Here is an explaination of sudo





Don't Log in as Root

An excellent way to find yourself in deep trouble is to modify permissions as root. Logging in as root means you will be browsing the Internet as root, drive by downloads (downloads that you did not authorize or that you authorized but did not realize the consequence behind), malicious scripts can all now execute with root permission. Default settings in Ubuntu will not allow you to log in as root.





Encrypt Your Home Folder

Encrypting the home folder will help for physical security. If someone is able to sit down in front of your computer or if they steal it, they won't be able to see the files in your home folder. In Ubuntu when you encrypt the home folder, the folder mounts when you log in which makes it readable to anyone sitting in front of your computer. Once you log out, the home folder unmounts and is encrypted again. Encrypting the home folder will do nothing to protect you from on-line threats. As long as the encrypted folder is mounted, it will be plain text for anyone with access.

You can encrypt your home folder or the entire hard drive on first install. Alternatively you can click here and here to learn how to add encryption to your home folder after installation. You could even just encrypt a particular file, a sub-directory, a usb stick... the choices are endless.



There are risks with encryption, so carefully evaluate your personal situation to determine if it is right for you. If you lose the password then your chances of recovering the data drop to almost nil. You should also keep in mind that if you encrypt your home folder or hard drive, that if your system fails later on it will be harder to recover your files. You will have to consider the value of the data you store on your computer to determine if encryption is worth the risk. For instance, if you insist on saving a detailed list of all your financial accounts in a text file, then encryption is vital. But if you don't store anything of personal value on the hard drive, then encryption may be less necessary.





Least Privileges, Always

Always make sure you are using the least amount of privileges/permissions to do the task necessary. Use only what you need, nothing more. If you are surfing the net and come across a "drive-by download" site, then what the malicious program has access to changes dramatically if it has lowered privileges. Learn how to use file permissions and non-privileged users (which Ubuntu makes very easy). Here is a link to everything you need to know about file permissions. Also consider enabling guest accounts if you will have other people using your computer.





Security updates are released by Ubuntu developers when they discover and patch vulnerabilities. If you don't install the updates then you retain the vulnerability. Ubuntu allows you to have security updates automatically installed - once configured you don't need to run security updates manually again. Search for the Update Manager on your desktop and click on "settings" to configure how you want Ubuntu to manage updates. Or you can configure automatic updates via terminal.





Know What You Have, Have What You Know

Don't run services you don't need. Do you really need a VOIP phone system? What about Secure Shell (SSH), Virtual Network Computing (VNC), Apache server? If you need a service, make sure you understand it and can properly secure it. You can't secure what you don't understand.





Make Your Browser More Secure

The majority of threats to your machine come from your browser, even when you use common sense. You have absolutely no control over vulnerabilities on someone else's web page as an end user, so it's important to defend yourself against any malicious activity originating from a compromised web page. If you are interested in learning how browser exploits happen, you can read this summary of the top ten vulnerabilities in a poorly designed web page.



Secure your browser. We will discuss Firefox because that's the browser packaged in Ubuntu. However, other browsers have similar features. We recommend that you use the following services. As mentioned before, these measures may inhibit functionality until you manually configure them. Again you must weigh the need for security against the need for functionality as it relates to your personal situation.



Preferences

Find Preferences in the menu bar of Firefox. Under the privacy tab you can tell web sites you don't want to be tracked and you can choose to never remember history. You can choose to whitelist sites for specific needs using exceptions, allow for session at most; clear history when closing the browser. Choose "never remember history" so that if someone hijacks your browser section, they won't find any valuable stored data. Don't use "hardware acceleration".



NoScript

If you unknowingly visit a compromised website, this will prevent scripts (i.e. programs) from running on your system. It can be a tricky tool to use at first glance as it blocks all scripts from running at first. If you spend a little time getting familiar with NoScript, you will find it easier to use. As a user, you tell NoScript what sites to partially or fully trust. Don't "allow all scripts globally" under any circumstances!



Configuring NoScript is notoriously daunting to the new user. A helpful guide to configure NoScript is included on a separate page, https://wiki.ubuntu.com/BasicSecurity/NoScript.

AdBlockPlus

You can tell by the name that it (surprise!) blocks annoying ads, but it can also block those ads from collecting personal information about you. Adblock Plus provides a default list of blocked ads. Additionally, you can block any individual ads or scripts that show up by adding them manually.



BetterPrivacy

The add-on BetterPrivacy will prevent websites from installing “super cookies” on your computer designed to track your history for marketing research.



ClickClean

ClickClean is a simple tool to delete your browsing history, erase all temporary internet files, remove downloaded files history, cookies, Flash LSO, typed URLs. Allows for automatic deletion of private data when Firefox closes. Basically if your browser session is ever hijacked, then the hijacker will get little valuable information.





The importance of securing your browser cannot be overstated. We've listed some of the simple tools you can implement to drastically improve your security. There are numerous others aimed at security as well as privacy, we encourage you to research those.





Home Network

Most computer users at home have a local network...often without even realising it. We encourage you to learn more about securing your home network - again, you can't secure what you don't understand. The CERT Guide to Home Network Security provides an excellent overview of the basic principles of networking and the internet. Learn some of the fundamentals about securing your router. For instance, if you use wireless access, make sure you're using STRONG encryption: not WEP but WPA/WPA2. Use a GOOD password consisting of all 63 characters, you only have to type it once anyway.



Devices plugged into your network can be accessed by unauthorized users just as easily as your computer can. Learn about making a networked printer more secure.





Repeating All of the Above on Each System

Be consistent, if you do these things with your desktop Ubuntu system you will find it is actually pretty secure. If you have two computers running Ubuntu, then repeat this process on both computers. If you've got one computer partitioned, then secure all partitions. Now apply this to the other devices on your network. This includes any other computers, cell phones, routers, printers, game consoles whatever. Your network's security is only as strong as the weakest link.





So that was the "easy" stuff. True security is an ongoing process, and a lot of the really good security tools require regular interaction from you. The next tools we describe are more advanced because you cannot "set and forget" them. They also require more effort to setup and use effectively, but the effort is worth it. The more security measures you implement from this Wiki, the more secure you will be.





Firewall

There is a lot of existing information about firewalls - along with a long-term raging debate on the need of a firewall on Ubuntu. We recommend you enable it because you have ports open if you are reading this page. Traffic can go in and out of that port unhindered without a firewall. Malicious programs can open arbitrary ports unless you have a firewall to prevent that. A NAT router can add a layer of protection, but it will not protect you in lieu of a firewall. This additional guide will provide more information.



Use your firewall PROPERLY. Don't set it and forget it, learn how it works, set decent rules.Here is a tutorial showing how to enable a firewall in Ubuntu. However, adding port numbers can feel confusing. It if helps, think of it this way - currently you're reading this guide because you accessed a webpage hosted by wiki.ubuntu.com. To make the connection (and therefore to see the content) you have to connect your browser to that website by accessing Port 80. Another example is when you pick up your email. Your computer makes a connection to your mail server on Port 110. The other port numbers that you add provide similar functions.





AppArmor

AppArmor can strengthen our security. To quote the Novell site, "AppArmor is designed to provide easy-to-use application security for both servers and workstations. Novell AppArmor is an access control system that lets you specify per program which files the program may read, write, and execute. AppArmor secures applications by enforcing good application behavior without relying on attack signatures, so it can prevent attacks even if they are exploiting previously unknown vulnerabilities." AppArmor has a pretty steep learning curve for new users. However, once you master it, creating profiles for most applications is fairly simple. It only gets tricky when you deal with applications that have to change functions a lot (for instance, Apache). Here is a tutorial on AppArmor.





Did I Just Get Owned?

For a helpful guide created by Dangertux which can help you determine if you have been compromised, see this page:

https://wiki.ubuntu.com/BasicSecurity/DidIJustGetOwned

Acknowledgements

This Wiki was birthed on the Ubuntu Forums by MrLeek and Ms. Daisy. Contributions came from Dangertux, OpSecShellShock, haqking, Thewhistlingwind, dFlyer, vasa1, Olle Wiklund, CharlesA and a Mystery Guy



