WordPress cross-site scripting (XSS) attacks: how to protect your site.

Cross-site scripting (XSS) attacks are one of the most common WordPress security threats admins and users face, mainly because the flaws that allow them to occur are widespread across websites, themes, and plugins.

This article will explore the following: 

• What XSS attacks are.
• What hackers gain from XSS attacks.
• The types of XSS attacks.
• How common of a threat XSS attacks are for WordPress sites.
• Security measures you can take to protect your WordPress site from them.

This will be an introduction to XSS attacks and how you can minimize the chances of suffering one. Let’s get into it.

What are cross-site scripting (XSS) attacks?

XSS is a malware attack where a third party injects malicious scripts into otherwise benign but vulnerable WordPress websites. The injected scripts can track and impersonate legitimate users, steal sensitive data, redirect a website, and more.

Cross-site scripting attacks are not limited to the WordPress ecosystem. Still, many plugins, themes, and website elements contain vulnerabilities that hackers can exploit to inject malicious code.

Due to the high number of vulnerable entry points, XSS attacks are one of the most common ways hackers break into WordPress sites, and they’ve become even more common in recent years. Admins and users must be aware of XSS attacks and know how to prevent them.

How do WordPress XSS attacks work?

XSS attacks can be hard to understand for users and admins who aren’t very tech-savvy, so it’s essential to take some time to know the basics.

Scripts

In software development, a script is a sequence of instructions executed by a computer program like a desktop website or a mobile app.

You can create simple, harmless scripts that add and multiply numbers, but you can also create more complex, harmful scripts that monitor and steal data. XSS attackers use harmful scripts.

How XSS attackers use malicious scripts

In XSS attacks, hackers use one or multiple of the website’s input fields (comments, review sections, search bars, personal information forms, etc.) to inject malicious scripts, usually written in JavaScript. For example, a hacker could access a website and leave the following comment in a blog post’s comment section:

<script src=“malicious_code_information”><script>

In “malicious_code_information,” the hacker would leave information (IP address, port number, etc.) that leads to a server they have access. If a website does not have protections to defend itself against these tactics, the malicious script will become embedded in the webpage it was injected into, allowing hackers to monitor user data.

The root of the vulnerability is often that the website does not validate or encode user data. This means they do not check data inputs for invalid, malicious sequences or enforce a specific format when transmitting data. By exploiting these flaws, hackers introduce malicious code into websites users trust and wouldn’t expect to be hacked.

What do hackers gain from XSS attacks to WordPress sites?

XSS attacks are often gateways to future attacks because they establish unauthorized backend access. From there, hackers can run additional malicious software, allowing them to steal user and admin data and credentials they can use later or sell for profit.

Through an XSS attack, hackers can:

• Redirect users to phishing sites or fake login pages where they’ll steal user credentials.
• run additional scripts, like sending fake pop-ups that ask for and collect personal information such as Facebook or Google user and password. They can also collect email addresses, IP addresses, credit card data, and other information users share with compromised sites.
• Steal users’ cookies, allowing them to access other web applications with those credentials.
• Spread more malware on the site, set up unauthorized ads they can profit from, deploy SEO spam attacks, route traffic to their own web domains, or enact a ransomware attack.
• Install keyloggers, programs that record and collect every user keystroke, effectively recording everything they type on site.
• Hijack the site for purely malicious purposes.

Types of XSS attacks

Reflected XSS

Also known as non-persistent or Type I XSS attacks, this kind of XSS attack “reflects” malicious code off a website and into the user’s browser. Most of the time, reflected XSS attacks work like this:

1. The hacker creates a malicious link by adding fields with malicious code into an otherwise benign URL, fill-in form, search result, or error message (like a 404 page).
2. The site user is tricked into clicking the link. By doing this, the user requests malicious content from the website’s server.
3. The website’s server returns the requested resources, including the malicious code injected by the hacker. This is part of the attack where the “reflected” name comes from.
4. The browser receives and runs the malicious script like every legitimate page element.
5. The script steals personal information from the user.

This kind of XSS attack generally requires some degree of social engineering. That is, tricking the user into clicking a link they assume is safe to steal their data. This can happen through an email, pop-up message, or any other web interaction where the user has to click a link to move forward.

Unlike the next type of XSS attack, in reflected attacks, the malicious code is never stored in the server long-term.

Stored XSS

Also known as “persistent” or “Type II” XSS attacks, this type of attack effectively “plants” malware into the target website. The example above about leaving a comment with malicious code is an example of a stored XSS attack.

In these attacks, hackers introduce a script that’s stored (hence the name) in the target website’s server by leaving a comment, review, forum post, etc., on the site. The script can stay on the server long-term or even permanently if not detected. 

Users interacting with the malicious script’s location are vulnerable to losing personal information. Hackers can configure the script, so visitors compromise their credentials by simply clicking or hovering the cursors over a specific page element. Hackers can also program the script to execute as soon as the page loads.

Due to their nature, stored XSS can be hard to spot and wreak all sorts of havoc in the meantime.

DOM-Based XSS

Also known as a “Type 0” attack, this kind of XSS attack is unique in that there is no direct interaction with the website’s server. In reflected and stored XSS attacks, the malicious code always interacts with the server in some way, either by being stored in it or sneakily sent to the user when responding to a request.

DOM-based XSS attacks rely on manipulating the web browser’s Document Object Model (DOM), a hierarchical representation of the elements of a webpage. Hackers can modify a browser’s DOM with JavaScript to inject malicious code.

One of the main problems that leave the door open to this attack is that many websites use very little HTML and instead rely on a lot of JavaScript code to handle user interactions with the webpage. This is a great way to minimize server overhead because most of the interactions are handled on the user’s browser rather than costing server resources, but it also opens websites to a lot of vulnerabilities.

DOM-based XSS attacks occur when JavaScript code accepts user input (source) and passes it as part of an unsafe function that is displayed back to the page (sink). “Unsafe” functions don’t perform security checks on the input before displaying it on the page.

When an input isn’t checked for malicious code, hackers can run pretty much whatever they want, including scripts that monitor and collect user data.

How common are XSS attacks in WordPress?

XSS attacks are one the most common methods hackers use to crack website security because many website elements contain vulnerabilities that allow third parties to introduce malicious scripts.

According to Wordfence’s 2022 security report, XSS attacks were the most common category of vulnerability disclosed during 2022, accounting for nearly half of all vulnerabilities disclosed that year.

One of the main problems around XSS attacks is that they can be present on any website, popular or not. In their 2021 report, Sucuri determined that the plugin Astra Starter Templates was one of the ten most vulnerable plugins based on their popularity. With over one million installations, this plugin’s XSS vulnerabilities represented a significant security threat for many WordPress users and websites.

How to prevent WordPress XSS attacks? 7 ways to protect your WordPress website

You can take multiple measures to take away chances for hackers to exploit WordPress vulnerabilities. The following are the most significant.

Update plugins and themes

Keeping plugins and themes updated is one of the best ways to avoid the vulnerabilities of older versions.

When developers release a security patch, they reveal the vulnerabilities they’ve found, which they’ve corrected for the newest version. Once the past vulnerabilities become public, websites using past versions of those plugins and themes become a target for hackers exploiting security flaws.

Install web application firewalls (WAF)

WAFs are evolutions of the traditional hardware firewalls that control data flow at the IP address and transport protocol levels. WAF can filter attacks performed at the application level, where applications run code and perform functionality on the web server. This is where XSS attacks are performed.

WAFs can detect unusual input in website textboxes to prevent SQL injections, XSS attacks, and more. Investing in a plugin that provides WAF services will boost your website’s security and prevent XSS attacks.

Install a trusted security plugin.

Explore the marketplace for a security plugin that detects malware attacks like XSS. High-quality security plugins perform regular scans and detect unusual activity. Some of the benefits include:

• Protecting confidential information.
• Stopping other security threats such as brute force attacks.
• Protecting your SEO rankings by repelling hacking attempts.
• Spam filtering.
• Two-factor authentication on logins.

Sanitize user inputs

As we explained before, one of the main vulnerabilities XSS attacks exploit is the lack of input validation and sanitization some websites suffer from. “Sanitizing” means removing unsafe characters from user input and validating enforces specific data formats and types.

Given how many XSS attacks rely on poor input monitoring practices, this measure will significantly protect your website.

Implement WordPress hardening

WordPress hardening is a series of security measures that increase the overall security of your site. Some of those measures include ones we’ve mentioned before, such as installing a security plugin.

These are some WordPress hardening actions you can take to make your website more secure from XSS attacks and cyberattacks in general:

• Use and require strong passwords by not allowing passwords that are easy to crack.
• Install SSL certificates.
• Enforce two-factor authentication.
• Limit login attempts.
• Automatically log out inactive users after a certain period.
• Install an audit log to record every action users take on your site.
• Disable the file editor to prevent unauthorized users from changing your site’s layout.

Make frequent backups

Whether through a backup plugin or your web host, backing up your website frequently can help you roll back your site in an emergency.

Limit admin permissions to the minimum necessary.

If multiple admins use your site daily, you should limit their permissions to what is strictly necessary for their role. If an XSS attack obtains admin credentials, the changes they can make are limited to the permissions of the user they hijacked.

Keeping permissions restricted to what’s strictly necessary helps minimize breaches if admin credentials are compromised.

Conclusion

WordPress admins and users must be aware that XSS attacks are one of the most common. They’re difficult to defend against because many software components contain vulnerabilities that allow hackers to inject malware into a site.

Due to how widespread these security flaws are, it’s a challenge to 100% protect your site from XSS attacks. However, taking the described measures can protect yourself from the most common break-in methods.

By reading this article, you’re now more aware of the vulnerabilities hackers exploit when deploying XSS attacks and can start taking action to prevent them.

If you found this post useful, read our blog for more WordPress insights, guides, and tips.