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
PricingFree downloadThe WordPress.org download is free. Pro versions, add-ons or external services may cost extra.
CompatibilityRequires WordPress 5.9 and PHP 7.4.
SourceWordPress plugins · Nov 14, 2026
01 / Source details
Aboutthistool.
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.
04Unsafe hashes / Inline styles Sometimes, HTML elements as images or buttons use HTML Event Attributes (onclick, onsubmit…) to let events trigger actions in a browser. You cannot use hashes or nonces for script included in event attributes and, adopting a strict CSP, requires refactoring those patterns into safer alternatives or to use ‘unsafe-hashes’. You got a similar problem when inline styles are used in HTML tags: <h1 style="color:blue;text-align:center;">This is a heading</h1> <p style="color:red;">This is a paragraph.</p> CSP Level 2 browsers may be ok with just putting the hash in your style-src directive. However, to allow hashes in the style attribute on inline CSS on browsers that support CSP Level 3, you may get an error like this Refused to apply inline style because it violates the following Content Security Policy directive: "style-src 'self' 'sha256-nMxMqdZhkHxz5vAuW/PAoLvECzzsmeAxD/BNwG15HuA='". Either the 'unsafe-inline' keyword, a hash ('sha256-nMxMqdZhkHxz5vAuW/PAoLvECzzsmeAxD/BNwG15HuA='), or a nonce ('nonce-...') is required to enable inline execution. To allow inline styles you need to use ‘unsafe-hashes’ in your style-src directive (that is, in facts, unsafe). ^
This plugin approach
This plugin affords those problems in this way:
05During a capture phase, it detects the scripts, styles and other embedded content present in the pages of your site and stores them in the database.
06Then you have to whitelist these contents from plugin admin.
07The plugin uses machine learning to cluster inline scripts trying to aggregate scripts generated by the same server side (PHP) code. So, you can authorize one script example to authorize all scripts that the classifier predicts to label as whitelisted clusters.
08You can choose to use hashes to authorize external scripts (and the plugin will allow you to include Subresource Integrity in your <script> and <link> )
09You can use hashes or nonces to authorize inline scripts.
10You can ask the plugin to refactor your page to not use event attributes (converted in a inline script) and inline styles (converted in an internal CSS).
11You can set one or more violations’ report endpoints.
The plugin supports multisite installations and has (too) many options documented in inline help.
Creating a Content Security Policy
After plugin activation, go to Settings menu and search for CSP Settings submenu. The steps you are supposed to do are the following.
12From the Tools tab, activate the capture of the tags and use your site by visiting all the pages or having your users visit them for a long time long period based on the use of your site (hours or days).
13From the Tools tab, perform the data clustering in the database (it can use many server resources).
14Go to the Base rules tab and include in the CSP directives the desired values (help you with the table at the bottom of the page).
15Go to the external scripts tab, inline scripts tab and scripts invoked by event handlers tab and authorize the execution of all the legitimate scripts present on the pages of your site.
16Leaving the tag capture active, activate the policy test (at this stage the plugin will generate some violations of the temporary policy used to record additional values to be included in the directives of your “content security policy”).
17After visiting again your site pages, disable the capture of the tags and repeat the previous steps 2, 3 and 4.
18Enable site protection.
N.B. When you update plugins or themes, if something doesn’t work properly on your site pages, temporarily deactivate the protection and repeat steps 1 to 7.
Plugin hooks
Filters
nunil_output_csp_headers_header_csp nunil_output_csp_headers_header_csp is available since version 1.2.3 and can be used to modify the Content-Security-Policy header before it is sent to browser
no_unsafe_inline_not_sri_sources no_unsafe_inline_not_sri_sources can be used to modify the list of external resources that do not support SRI (Subresource Integrity)
no_unsafe_inline_final_output no_unsafe_inline_final_output is an internal filter used to manipulate the output of the WordPress process just before the output is sent to the browser.
no_unsafe_inline_meta_injector no_unsafe_inline_meta_injector is an internal filter hook used to inject meta http-equiv=”Content-Security-Policy” if variable is set
Actions
nunil_upgrade Functions hooked on nunil_upgrade will run when the plugin is upgraded
nunil_output_csp_headers Functions hooked to nunil_output_csp_headers will run when the plugin output the CSP HTTP response header
Code and libraries
This version of the plugin uses: * to parse HTML: * ivopetkov/HTML5DOMDocument on PHP<8.4 and libxml<=2.13.09 * Masterminds\HTML5 on PHP<8.4 and libxml>2.13.09 * \Dom\HTMLDocument : The new ext-dom features with HTML5 support on PHP>8.4 * RubixML for machine learning from version 1.1.0 – PHP-ML was used in versions 1.0.x ; * opctim/php-nilsimsa to calculate and compare Nilsimsa digests.
The log functions have been taken from * perfectyorg/perfecty-push-wp , something you should really try if you want to implement web Push notifications in your site.
The complete list of dependencies used in this plugin can be seen in dependency graph on GitHub.
Contributions, Issues, Bugs
Plugin code is hosted on a public repository on GitHub . Reach me over there to help and suggest.
See it in action
Screenshots & previews.
Plugin's tools tab in a multisite enviroment.External scripts tab.Inline scripts/styles tab.List of CSP directives managed in Settings tab.A database summary table at the bottom of tools tab.
02 / Source details
Gettingstarted.
Automatic installation
01Plugin admin panel and add new option.
02Search in the text box No unsafe-inline .
03Position yourself on the description of this plugin and select install.
04Activate the plugin from the WordPress admin panel.
Manual installation of ZIP file
05Download the .ZIP file from this screen.
06Select add plugin option from the admin panel.
07Select upload option at the top and select the file you downloaded.
08Confirm installation and activation of the plugin from the administration panel.
Manual FTP installation
09Download the .ZIP file from this screen and unzip it.
10FTP access to your folder on the web server.
11Copy the whole no-unsafe-inline folder to the /wp-content/plugins/ directory
12Activate the plugin from the WordPress admin panel.
03 / Source details
Frequently asked questions.
Is this plugin easy to use?
This is not a click and go tool, but you can follow the instructions and implement a strict CSP.
Has this plugin been widely tested?
No.
Will this plugin impact the site’s performance?
During capturing phase this plugin needs to write many data to database, so your site can slow down. When the plugin enforces the CSP, it uses a mu-plugin to capture the output of the WordPress process, manipulate it and then send to browser. I don’t have any measure of inherent overhead.
Is there another way to implement a strict content security policy in WordPress?
Not in my knowledge.
Do you offer professional support for this plugin?
No. But I do my best to offer free support on wordpress.org support forum in my spare time.
FinderPress Media Auditor helps site administrators scan for broken images, missing Media Library files, unreachable media URLs, and other media issues across WordPress content. Use it to audit images, video, audio, PDFs, featured images, and attachment files without sending scan data to an external
The Accepted Payment Methods plugin is a straightforward, lightweight solution that enhances your website by displaying visually appealing icons of the payment methods you accept. This plugin is ideal for a variety of websites, including e-commerce platforms, service-oriented websites, and informati
