What Is XSS?

The threat of a cyber attack can strike terror in the hearts of anyone who spends time online. From hacks against individuals like phishing schemes or evil twinning, to large scale cyber attacks such as malware and ransomware, it seems like malevolent hackers lurk in every corner of the Internet.  

The good news is that once you’re cognizant of online threats, you can better protect yourself against the harm they can cause. XSS, also known as cross-site scripting, is an attack that exploits gaps in the security of a website by injecting malicious code. Let’s take a look at the ways XSS can expose your site’s weaknesses and how you can protect yourself from ruinous damage.

What is an XSS attack?

An XSS attack is an injection of malicious or “bad” scripts and code into the browser of the user. The “injection” occurs on a credible website with a security flaw. If a website hasn’t been audited, its security weaknesses may remain undetected. The website’s owner remains unaware as the cross-site scripting slowly attacks the browsers of each user to visit the site.

The XSS sounds deadly, and, it can be, figuratively — as the injected script can spread quickly to multiple website visitors. Your browser only sees that a script from a verified website is trying to transmit, so it allows the script through. XSS can steal the cookies of your current online session, and any sensitive data stored in your browser history.

How does an XSS attack work? 

Cross-site scripting typically uses JavaScript to inject into its targeted websites. Bad online actors can inject the script via user-input pages on the site. The attack can then automatically go into effect when a user clicks on the website or hovers over a specific section. 

Although the attack doesn’t necessarily directly harm a website owner, it can have dire consequences for visitors to an attacked site. Some XSS attacks can lead to:

• Taking a user from the credible site to a malicious, unsecured site
• Completely crashing your browser
• Stealing your active cookie and potentially the data you use to log in to the infected website
• Compromising your account and stealing your credentials 
• Using your personal information to create phony accounts on other websites

Types of XSS attacks

XSS attacks can occur via several different methods. The most common types of attacks include:

DOM-based XSS

A DOM-based (Document Object Model) XSS attack only occurs after a web page has been loaded. DOM-based attacks are cross-site scripting. Although a site’s HTML code doesn’t change, the malicious injection of script goes undetected. The attack is triggered by the users’ side of connection which means the exposed weakness is on the client’s side rather than the server’s side.

Reflected XSS 

A Reflected XSS attack bounces off of a website application and infiltrates a user’s browser. This type of attack usually comes through an embedded email from the site or in a social media post’s comment thread. For instance, if you’re commenting on a public page and see an irrelevant comment about a “witch doctor who can work miracles,” you should refrain from clicking on this comment or any link it shares.

Stored XSS

Stored XSS attacks (or Type-1 XSS attacks) use a website’s permanent scripts as an injection point. Hackers launching a Stored XSS attack control how browsers execute their malicious scripts. These attacks can totally take over your account. 

What are some examples of XSS attacks?

Over the past decade, large scale XSS attacks have occurred globally and include well-known targets. Some of the biggest cross-site scripting attacks include:

British Airways XSS Attack

In 2018, an organized hacker group called Magecart claimed responsibility for a targeted XSS attack against British Airways. The airline used a JavaScript known as Feedify on its website and Magecart injected malicious script into the program’s vulnerable spaces. Customer data was then sent to a bogus website that mimicked British Airways. 380,000 customers experienced credit card skimming as a result.

Fortnite XSS Attack

The wildly popular interactive multiplayer online game was the target of an infamous XSS attack in 2019. 200 million players had their personal data exposed to hackers.

T-Mobile XSS Attack

Although T-Mobile has addressed their enormous security breaches of 2021 and 2023, the company hasn’t publicly stated what type of cyber attack was responsible. The exposed data of over 100 million customers (76 million in the 2021 attack and 37 million in 2023) may have occurred as the result of an XSS attack. 

How can you prevent an XSS attack? 

Over 60% of all website applications are susceptible to cross-site scripting attacks. Although XSS attacks can occur at any time and 100% prevention may feel impossible, there are measures you can take to help protect yourself against them. If XSS does hit your website or browser, you can also take steps to mitigate the damage.

Steps to take against an XSS attack include:

• Test your browser by injecting your own payload (transmitted code and data) to simulate a cross-site scripting attack with random JavaScript or another scripting application. Do this via the alert or print function, so your browser can recognize warning signs of bad JavaScript

• Use a security filter on your website that prevents user input from injecting questionable code.

• Create your website to require validated data. For example, require all input data to be validated or rejected.

• Ensure your software updates with every new security patch offered. It’s easy to forget to continually update your personal operating system, but it’s vital for protection from XSS attacks. If you run a business and don’t employ an IT or cyber security team, it’s important to make sure you delegate security updates to someone with computer skills.

• Perform regular security scans of your operating system. You should scan for vulnerable areas weekly, if not daily.

• Sanitize your data. Look for unknown HTML tags and characters and remove them from your data logs.

• Install a Web Application firewall. These firewalls, such as Cloudflare Spectrum, block bots and can weed out malicious scripts.

Although cybersecurity requires due diligence, understanding the different types of attacks you may face allows you to take appropriate security measures. 

What’s My IP Address offers tools to help you  keep track of data breaches and protect your online security. For example, our Breach Check alerts you to database attacks so you can stop them before havoc is wreaked.

Now that you understand what XSS is, check out our blog for a thorough look at other cybersecurity threats and how to prevent them.