Really Simple Security – Simple and Performant Security (formerly Really Simple SSL) vs 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 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 Manual 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 , 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. Inline 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”. WordPress 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 doWhatever(); and in your script-src directive: script-src 'nonce-rAnd0m'; And, of course, a nonce must be unique for each HTTP response. Unsafe 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: This is a heading This is a paragraph. 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: During 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. Then you have to whitelist these contents from plugin admin. The 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. You can choose to use hashes to authorize external scripts (and the plugin will allow you to include Subresource Integrity in your and ) You can use hashes or nonces to authorize inline scripts. You 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). You 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. From 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). From the Tools tab, perform the data clustering in the database (it can use many server resources). Go 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). Go 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. Leaving 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”). After visiting again your site pages, disable the capture of the tags and repeat the previous steps 2, 3 and 4. Enable 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 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.

Easily improve site security with WordPress Hardening, Two-Factor Authentication (2FA), Login Protection, Vulnerability Detection and SSL certificate. Really simple, Effective and Performant WordPress Security Really Simple Security is the most lightweight and easy-to-use security plugin for WordPress. It secures your WordPress website with SSL certificate generation, including proper 301 https redirection and SSL enforcement, scanning for possible vulnerabilities, Login Protection and implementing essential WordPress hardening features. We believe that security should have the absolute minimum effect on website performance, user experience and maintainability. Therefore, Really Simple Security is: Lightweight: Every security feature is developed with a modular approach and with performance in mind. Disabled features won’t load any redundant code. Easy-to-use: 1-minute configuration with short onboarding setup. Security Features Easy SSL Migration Migrates your website to HTTPS and enforces SSL in just one click. 301 redirect via PHP or .htaccess Secure cookies Let’s Encrypt: Install an SSL Certificate if your hosting provider supports manual installation. Server Health Check: Your server configuration is every bit as important for your website security. WordPress Hardening Tweak your configuration and keep WordPress fortified and safe by tackling potential weaknesses. Prevent code execution in the uploads folder Prevent login feedback and disable user enumeration Disable XML-RPC Disable directory browsing Username restrictions (block ‘admin’ and public names) and much more.. Vulnerability Detection Get notified when plugins, themes or WP core contain vulnerabilities and need appropriate action. Login Protection Allow or enforce Two-Factor Authentication (2FA) for specific user roles. Users receive a two-factor code via Email. Improve Security with Really Simple Security Pro Protect your site with all essential security features by upgrading to Really Simple Security Pro. Advanced SSL enforcement Mixed Content Scan & Fixer. Detect files that are requested over HTTP and fix them to HTTPS, both Front- and Back-end. Enable HTTP Strict Transport Security and configure your site for the HSTS Preload list. Firewall Really Simple Security Pro includes a performant and efficient WordPress firewall, to stop bots, crawlers and bad actors with IP and username blocks. 404 blocking – Blocks crawlers as they trigger unusual numbers of 404 errors. Region blocking – Only allow/block access to your site from specific regions. Automated and customisable Firewall rules. IP blocklist and allowlist. Security Headers Security headers protect your site visitors against the risk of clickjacking, cross-site-forgery attacks, stealing login credentials and malware. Independent of your Server Configuration, works on Apache, LiteSpeed, NGINX, etc. Protect your website visitors with X-XSS Protection, X-Content-Type-Options, X-Frame-Options, a Referrer Policy and CORS headers. Automatically generate your WordPress-tailored Content Security Policy. Vulnerability Measures When a vulnerability is detected in a plugin, theme or WordPress core you will get notified accordingly. With Vulnerability Measures, you can configure simple but effective measures to make sure that a critical vulnerability won’t remain unattended. Force update: An update process will be tried multiple times until it can be assumed development of a theme or plugin is abandoned. You will be notified during these steps. Quarantine: When a plugin or theme can’t be updated to solve a vulnerability, Really Simple Security can quarantine the plugin. Advanced Site Hardening Choose a custom login URL Automated File Permissions check and fixer Rename and randomize your database prefix Change the debug.log file location to a non-public folder Disable application passwords Control admin creation Disable HTTP methods, reducing HTTP requests Login Protection Secure your website’s login process and user accounts with powerful security measures. Two-Step verification (Email login) 2FA (two factor authentication) with TOTP Passwordless login with passkey login Enforce strong passwords and frequent password change Limit Login Attempts With Limit Login Attempts you can configure a threshold to temporarily or permanently block IP addresses or (non-existing) usernames. You can also throw a CAPTCHA after a failed login (hCaptcha or Google reCaptcha) Access Control Restrict access to your site for specific regions. Add specific IP addresses or IP ranges to the Blocklist or Allowlist. Useful Links Documentation Security Definitions Translate Really Simple Security Issues & pull requests Feature requests Love Really Simple Security? If you want to support the continuing development of this plugin, please consider buying Really Simple Security Pro, which includes some excellent security features and premium support. About Really Simple Plugins Our mission is to make complex WordPress requirements really easy. Really Simple Security is developed by Really Simple Plugins. For generating SSL certificates, Really Simple Security uses the le acme2 PHP Let’s Encrypt client library, thanks to ‘fbett’ for providing it. Vulnerability Detection uses WP Vulnerability, an open-source initiative by Javier Casares. Want to join as a collaborator? We’re on GitHub as well!