How to Prevent XSS Attacks: Best Practices for Website Security | Blumira

We’ve gotten a lot of questions from people who have run a Domain Security Assessment on how to address the security gaps highlighted by their reports, and ”Lack of XSS protection” is one of the most frequent findings on that list. That shouldn’t be too surprising, given that injection-based attacks including cross-site script injection (XSS) remain #3 on OWASP’s top 10 list of web security vulnerabilities.

So, to help folks understand what XSS is, why it’s a risk, and how to protect your website, we put together a short explainer video you can check out below: 

If you’d like a skimmable breakdown of what the video covers, a bit more detail, or just prefer text to video… read on!

What Is XSS?

XSS attacks occur when someone injects code (usually JavaScript) into legitimate websites that then executes in visitors' browsers. If the site isn’t properly secured, the visitor’s browser can't distinguish between legitimate site code and the injected malicious script — it all runs with the same permissions and access to cookies, session tokens, and other sensitive information as the legitimate site.

In the video, we show a simple visual example (which also functions as a common test whether a site is vulnerable to XSS attacks): a blog comment section where an attacker tags a string of JS to the end of their comment to create a pop-up alert. If the site doesn't properly sanitize this input, the attacker can “escape” that limited input field, their alert script gets interpreted as part of the page itself, and every visitor to that page could see that pop-up!

While a test alert saying "XSS test" might seem harmless, the same vulnerability could allow attackers to silently capture your authentication cookies and impersonate you on the affected site. This is particularly concerning for administrative accounts or sites handling sensitive information.

How To Prevent XSS Attacks On Your Domain 

Now, this blog is a designated FUD-free zone, so let’s talk about fixes! The good news is, defending against XSS attacks doesn't require a complete overhaul of your site. We cover three recommended best practices to reduce your risk:

• Implement Content-Security-Policy (CSP) headers – Define exactly which sources of content are allowed to execute in your users' browsers, effectively creating a whitelist that blocks unexpected script execution.
• Enforce HTTPS encryption – Secure all traffic with HTTPS and implement Strict-Transport-Security headers to prevent connection downgrade attacks and protect transmitted data.
• Set cookie security flags – Protect cookies from unauthorized access by blocking JavaScript access and implementing flags like HttpOnly and SameSite.

Protect your website from XSS attacks and other vulnerabilities. Run a free Domain Security Assessment today and get a detailed security report: