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WordPress is the most popular content management system (CMS), featuring a wide selection of customizable themes and plugins. However, this popularity also makes it a prime target for cyberthreats, including the infamous cross-site scripting (XSS) attack. This vulnerability exploit is a gateway to more severe security issues and must be treated as dangerous in its own right.
Whether you’re a WordPress site owner, web administrator or just interested in cybersecurity, understanding the nature of these exploits and how to defend against them is crucial.
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What Is Cross-Site Scripting?
XSS is a web security vulnerability that allows a cybercriminal to attach malicious code to a trusted site. This can be done in multiple ways. The most common involves inserting it at the end of a URL or posting it directly onto a page with user-generated content, such as contact forms and search fields.
The actual attack occurs when a visitor loads the website, which then executes the corrupted scripts and delivers the malicious active content to their browser. These exploits are possible across various scripting languages, though JavaScript is the most popular vector because it is fundamental to most dynamic browsing experiences today.
According to Patchstack’s 2024 web security report, XSS accounted for 53.3% of new vulnerabilities in the WordPress ecosystem.
Examples of XSS Attacks
A useful example of an XSS attack is on websites that allow users to post comments, such as forums and blog pages. In this case, the threat actor will enter their comment in the box as an executable code enclosed in ‘<script></script>’ tags. The tags prompt a user’s browser to interpret everything between them as JavaScript code and load it as the webpage is rendered.
Once that comment is posted, it infects the page, causing subsequent visitors to fall victim to whatever commands the code was intended to execute. For instance, the attacker can use that website to execute pop-ups requesting users to enter their login information. If they do, their credentials will be sent directly to the hacker, who can use them for various nefarious purposes.
Another example is using the XSS payload to steal web cookies — temporary data blocks identifying the user on a particular device. For instance, when you log into Facebook, the site gives you a cookie so that if you close the browser window and return later that day, you’ll still be logged in.
A hacker who gains access to these cookies could impersonate the web user to conduct social engineering attacks or steal sensitive data, such as geolocation coordinates and financial information.
Most Common Types of Cross-Site Scripting
Two common types of XSS vulnerabilities are reflected XSS and stored XSS.
Reflected XSS occurs when the malicious script is injected into a URL, so when the user clicks on the link, their browser executes the code. Threat actors typically use phishing tactics to trick victims. For example, someone might receive a legitimate-looking email asking them to take action on a bank’s website. In reality, the link has been compromised and will take them to a page where the hacker can retrieve any data the user accesses during the session.
Stored XSS, also known as persistent or second-order XSS, occurs when the malicious code comes from the website’s database. It’s “persistent” because the code keeps executing as long as users visit that page.
Why Is WordPress Particularly Vulnerable to XSS Attacks?
Several factors make WordPress sites attractive targets for XSS vulnerability exploitations. The main reason is its popularity. Since an XSS attack aims to compromise as many web visitors as possible, it makes sense that hackers will go for the service with the largest number of users.
WordPress comprises 43.4% of all websites and commands 62.8% of the CMS market share. Hostinger reports that over 10,000 WordPress websites are published daily through its hosting platform.
The abundance of plugins and third-party extensions can also be problematic from an XSS standpoint. While these add-ons are necessary for improving website functionality, they can also increase the attack surface, especially when developed without proper security measures.
Over 60,000 free plugins are available in the official WordPress directory, plus thousands of premium options sold by third-party developers. Any of these systems may have vulnerabilities that an attacker could exploit.
How to Protect Your WordPress Site Against XSS Attacks
There is no foolproof way to mitigate cross-site scripting, so your WordPress site must employ a mix of protection strategies.
Validate User Inputs
Validation involves implementing page interaction rules that prevent users from posting data that doesn’t meet predetermined criteria. This mostly applies to contact forms and comment boxes. For example, in the designated box for “First Name,” a validation rule could be set to reject any “<script>” tags or related characters.
Employ Data Sanitization
This entails treating any data received from users as potentially harmful and measuring it against a range of acceptable input. WordPress offers an array of built-in data sanitation functions, including sanitize_text_field() and wp_kses(), to sanitize input and filter out malicious code injections.
Implement Web Application Firewall (WAF) Rules
A WAF rule defines how to inspect traffic requests to a web application based on predefined inspection criteria. It also covers what conditions to look for in the request and what action the firewall should take when it matches the definitions. This security measure can help mitigate reflected XSS attacks as the WAF filters our malicious traffic, preventing the injected code from being executed.
Keep Your WordPress Site Updated
WordPress frequently releases updates that patch known vulnerabilities. For example, WordPress 6.5.2, released in April 2024, contains security patches to address the Avatar block type XSS vulnerability.
Only Use Secure Themes and Plugins
Some plugins and extensions may have poor coding practices or lack proper security measures. Always opt for well-reviewed, regularly updated themes and plugins from reputable sources. For instance, you can check a plugin’s download count and user reviews to get a better idea of its legitimacy.
What About Web Users?
Web users are the most affected by XSS attacks and must take measures to safeguard their browsing sessions. These include:
- Check for HTTPS in URLs: HTTPS means the website has an active SSL certificate, which encrypts data and prevents hackers from creating a fake version of the site.
- Change login credentials frequently: Users may have their credentials stolen in an XSS attack without even knowing. The general rule of thumb is to change passwords every three months to limit threat actors’ attempts to access an account.
- Take cookie security measures: Users can set special rules for handling their web cookies. For example, they can tie them to their specific IP addresses, so the information won’t be useful to the hacker, even if copied as part of an XSS exploit.
- Be wary of suspicious links: On average, 95% of security incidents begin with a phishing attempt. Web users can protect their computers and organizations from various cyberattacks by steering clear of suspicious URLs.
Protect Against WordPress XSS Attacks
Cross-site scripting is a major worry for WordPress site owners and administrators. Take advantage of these security measures to prevent attacks and ensure a wholesome browsing experience for your website.
