Many websites fail security header scans from tools like SecurityHeaders.com and the Mozilla Observatory.
Most of the time, the issues come down to missing or misconfigured browser-level headers rather than complicated technical flaws.
Once you understand what scanners look for and how browsers interpret these headers, improving your score becomes much easier. Each header acts as a small but important rule that shapes how your site behaves in a browser. Some prevent unauthorized scripts from loading, others block hidden frames, and some restrict what information is passed to other sites. Taken together, they create a safer environment for your visitors. Before adjusting them, it helps to understand the kinds of issues these headers are designed to protect against, which are explained in the sections below.
Cross-Site Scripting (XSS)
XSS occurs when attackers inject harmful JavaScript into a page, often through input fields, comments, search boxes, or third-party widgets.
If the browser runs this injected code, it can steal login cookies, redirect users, alter the page, capture keystrokes,
or impersonate users on your site. Security headers help control where scripts can come from, reducing the chance of malicious code executing.
Clickjacking
Clickjacking places your webpage inside a hidden or transparent frame on another site.
Users believe they are clicking a visible button, but they are actually interacting with an underlying element on your page.
This can lead to unintended actions, including form submissions, account changes, or financial transactions.
Headers such as X-Frame-Options and Content-Security-Policy’s frame-ancestors directive prevent your site from being framed elsewhere.
Content Injection
Content injection involves adding unauthorized scripts, images, text, or iframes into your pages through insecure code,
compromised third-party libraries, or unvalidated input.
Injected content can mislead visitors, display unwanted messages, load malware, or alter the layout of your site.
A strong Content-Security-Policy limits which sources are allowed, preventing most injected content from loading.
Data Leakage
When users click a link to another site, browsers may send referrer information. Without restrictions, this can include full URLs containing
query parameters or sensitive identifiers. A restrictive Referrer-Policy reduces how much information is shared, minimizing accidental data exposure.
MIME Type Guessing
If a server labels a file incorrectly, browsers may try to guess its actual type.
This guesswork can cause harmless files to be interpreted as executable or allow disguised malicious files to run.
The X-Content-Type-Options header prevents type guessing and forces the browser to trust the declared file type.
Unauthorized Use of Browser Features
Modern browsers provide access to features like the camera, microphone, geolocation, clipboard, and motion sensors.
If not restricted, any script running on your site could attempt to use these capabilities.
A Permissions-Policy header lets you explicitly choose which features are allowed, blocking unnecessary or unwanted access.
Mixed Content Vulnerabilities
If your site uses HTTPS but loads some resources over HTTP, attackers can intercept or modify those insecure files.
This can lead to altered images, injected scripts, or broken layout elements.
Headers like Strict-Transport-Security encourage browsers to use HTTPS for all resources, closing this loophole.
What Security Headers Are
Security headers are rules your server sends to a visitor’s browser before the page loads. They don’t change how your site looks, but they control how the browser handles things like scripts, frames, and sensitive data.
How Security Headers Work
These headers are included in the HTTP response your server sends. They’re typically added at the server level, which means they’re applied automatically to every page and file your site delivers. The browser reads them immediately and applies the rules before rendering anything on the screen.
- They’re automatically applied once configured at the server level.
- They don’t affect layout or site appearance.
- They can be tightened or relaxed as your needs change.
- They reinforce each other and strengthen overall security.
- They play a major role in header scan scores.
The Six Headers That Matter Most
Strict-Transport-Security (HSTS)
Enforces HTTPS and blocks insecure versions of your site.
X-Frame-Options
Prevents other sites from embedding your pages in frames.
X-Content-Type-Options
Stops browsers from trying to “guess” file types.
Referrer-Policy
Controls how much of the referring URL is shared with other sites.
Permissions-Policy
Restricts access to browser features you don’t need.
Content-Security-Policy (CSP)
Defines which sources your site is allowed to load scripts, images, and other content from.
Security Headers at a Glance
| Header | Primary Purpose | What Scanners Look For |
|---|---|---|
| Strict-Transport-Security | Forces secure connections | Long max-age, subdomain coverage, consistent HTTPS |
| X-Frame-Options | Blocks unauthorized framing | DENY or SAMEORIGIN |
| X-Content-Type-Options | Prevents MIME type guessing | nosniff |
| Referrer-Policy | Controls referrer data | Restrictive value such as strict-origin-when-cross-origin |
| Permissions-Policy | Limits use of browser features | Restricted access unless needed |
| Content-Security-Policy | Defines trusted content sources | No wildcards, no unsafe defaults, consistent rules |
Common Mistakes That Lower Scores
- Missing one or more essential headers
- Using outdated or permissive values
- Overuse of wildcard rules
- Weak or inconsistent CSP settings
- Not enforcing HTTPS
- Leaving unnecessary browser permissions enabled
- Partially configured or incomplete rules
How to Improve Your Header Scan Score
1. Run a Scan
Start by testing your site with SecurityHeaders.com or Mozilla Observatory.
2. Identify What’s Missing
Look for headers that are absent or values that scanners flag as weak.
3. Focus on the Six Core Headers
Updating these will resolve most scoring issues.
4. Choose Restrictive, Modern Values
Avoid permissive rules or outdated configurations.
5. Configure Headers at the Server Level
Once applied, the server sends these headers on every request automatically.
6. Test Again
Re-scan your site to confirm the changes took effect.
7. Adjust as Needed
CSP often requires refinement over multiple iterations.
8. Monitor Over Time
Security expectations evolve, so periodic checks keep your configuration current.
Why an “A” Grade Matters
A strong header score improves user trust, aligns your site with modern browser standards, strengthens your defenses against common web threats, and supports long-term reliability. Clean header configurations also help ensure compatibility with stricter environments and contribute to overall technical quality and compliance.
Security headers give browsers clear instructions that enhance safety without affecting your design or content. With the right configuration and occasional maintenance, earning an “A” is achievable and provides lasting value for your site.
If you’d like help reviewing your current configuration or want guidance on how to improve your header score, feel free to contact us anytime.