No unsafe-inline
Content Security Policy (CSP) is a computer security standard introduced to prevent cross-site scripting (XSS), clickjacking and other code injection attacks resulting from execution of malicious content in the trusted web page context. Cross-site scripting (XSS) is a type of security vulnerability
About this tool.
Content Security Policy (CSP) is a computer security standard introduced to prevent cross-site scripting (XSS), clickjacking and other code injection attacks resulting from execution of malicious content in the trusted web page context. Cross-site scripting (XSS) is a type of security vulnerability that can be found in some web applications. XSS attacks enable attackers to inject client-side scripts into web pages viewed by other users. A cross-site scripting vulnerability may be used by attackers to bypass access controls like the same-origin policy. Looking at National Vulnerability Database run by US NIST, more than 1100 (November 2025) vulnerabilities are reported as XSS for WordPress’ plugins and themes .
Keeping your site up-to-date with the latest versions of plugins and themes is the first line of defense to ensure your site’s security.
The second thing to do, is to deploy a strict Content Security Policy .
The main problem
The main problem with Content Security Policies implemented in the real world is that they are too weak to really protect your site and that many of them can be trivially bypassed by an attacker.
The proposed solution
Google researchers recommend, instead of whole host whitelisting, to activate individual scripts via a CSP nonces approach. In addition, in order to facilitate the adoption of nonce-based CSP, they proposed the ’strict-dynamic’ keyword.
The problem(s) with CSP in WordPress
- 01Manual creation of a policy Usually, a WordPress project is a mix of code written by different authors who contributed to the Core and or wrote plugins and themes. If it is possible to whitelist every external script loaded from a <script src=""> , the real truth is that in a WordPress project you can have dozens of those scripts included with your plugins and calculate a cryptographic hash for each of them to be included in your CSP header can be a frustrating job. However, there are many browser extensions and WordPress’ plugins that can help you in this job.
- 02Inline scripts WordPress core, and plugins, use inline scripts. For these scripts, you can compute hashes to be inserted manually into your policy, only if these scripts do not change at any page load. Unfortunately, this is not very common, as it is frequent to include variable values calculated server side in inline scripts. And it means that your inline scripts change too frequently to manually add their hashes to your policy. This commonly happens when scripts are “localized” .
- 03WordPress has no API to implement nonces for CSP Even if it is easy to generate a nonce for each page view, this nonce has to be inserted in every script tag used to embed inline scripts in your page as <script nonce="rAnd0m"> doWhatever(); </script> and in your script-src directive: script-src 'nonce-rAnd0m'; And, of course, a nonce must be unique for each HTTP response.
