How To Protect Your Website Against A Cross-Site Scripting (XSS) Attack

One of the most common methods that hackers use/will use to attack your website is a cross-site scripting (XSS) attack.

Basically, an XSS attack is where a hacker will take advantage of an XSS vulnerability to execute a malicious JavaScript when users visit your website.

The consequences of an XSS attack can be very drastic, ranging from the hacker spreading worms on your website, to the hacker stealing sensitive data that they can use for identity theft or financial crimes, to the hacker impersonating a user visiting your website by hijacking a progressing session.

It’s safe to say that an XSS attack is not something you will want to have happen to your website, which is why we will explain a number of different steps you can take to protect your website against it from ever happening to you.

But before we dive into that, it’s also important to fully understand how XSS attacks work in the first place.

How does an XSS attack work?

Cross-site scripting attacks are markedly different from either hacking attacks, like an SQL Injection, for the sole purpose that they are intended to attack the users of an application rather than the application itself.

How it works is the hacker will inject a code, such as a malicious JavaScript, into the output of an online application.

There are a number of vulnerable places they will be able to accomplish this in your website, such as in your search fields, your forums, or your cookies.

The primary aim of the hacker will be to collect cookie data, because cookies are often used to store sensitive information such as usernames and passwords or financial data.

To give you an idea of what a hypothetical cross-site scripting attack would look like on your website, let’s say that your website has a message board that allows visitors to submit comments.

The comments would be stored in a database online, and then be displayed to other visitors without any encoding.

A hacker would simply need to post a comment with a malicious script in it and enclosed by <script> tags.

When another visitor views the comment, the script will be executed and request the cookie information from the unsuspecting visitor. Furthermore, the script will be run under the context of a ‘secured website,’ so your browser will not be able to discriminate between content that is malicious and content that is legitimate.

This is ultimately just one type of XSS attack, referred to as a persistent XSS attack, but it is one of the most common.

Another way an XSS attack my occur (in a non-persistent XSS attack) is to try and deceive a website visitor into clicking a malicious URL, which would then inject a code into the page to give the hacker full access to its content.

Now that we know how XSS attacks work, we can begin to discuss some of the most effective steps you can take to prevent it from being a reality in your website.

Steps to prevent an XSS attack

Here are some different steps and strategies you can utilize to prevent an XSS attack and help keep your website data safe:

Use an SDL

SDL stands for ‘Security Development Lifecycle.’

You’ll specifically want to have used an SDL when developing your web application, with the main purpose of them being to limit the amount of coding errors and security flaws in your application, thereby making your website less vulnerable to an XSS attack.

In essence, an SDL will assume that all data your web application is receiving is coming from a source that can’t be trusted, even if that data comes from users who have logged themselves into your account multiple times.

This is exactly why an SDL will be beneficial in reducing XSS vulnerabilities, because as we have just looked at previously, an XSS attack can be launched against those who have already logged in.

Adopt a crossing boundaries policy

A crossing boundaries policy means that you make any authenticated users in your website have to re-enter their login information before they are allowed to access certain pages and services on your site.

Even if the authenticated user has a cookie that allows them to login automatically, you can still set it so that they have to re-enter their username and passwords anyway before entering certain pages.

The reason why this strategy is effective at stopping an XSS attack is because it strongly restricts the potential for a session being hijacked by an XSS hacker.

You can further expand on this concept to set it so that a session will be automatically expired when two IP addresses try to use the identical session data.

Use the right META tag

Here’s a meta tag that you can use on each page in your site to declare characters:

<META http-equiv="Content-Type" content="text/html; charset= ISO-8859-1">

The benefit to using this meta tag is that it will greatly reduce the number of potential forms that an XSS script injection can take.

Make use of a website vulnerability scanner

Last but not least, you can also make use of website vulnerability scanners when developing your web applications.

With a good vulnerability scanner, you can spot security weaknesses and flaws in your website, including those that are the most vulnerable to XSS hackers.

A vulnerability scanner will become even more important if you are using a third party package, in which case you may run into some configuration problems and you can’t assume that the package will be secured.

Conclusion

In conclusion, a cross site scripting attack is one of the most dangerous attacks that could happen on your website, with drastic consequences for your website that you won’t want to experience.

The good news is that no matter how dangerous an XSS attack may be, they are not something that you have to experience either, and you can take action to avoid them by following the steps that we have covered here today.