how to give random number to nonce in CSP

Question

Hi,

I am using a DevExpress MVC application, and I want to disallow the execution of unauthenticated inline scripts and styles. In one of the examples, I saw the following code

Can someone please check and help me find a way to assign a value to 'test-random-value' and outline the steps needed to implement this?

Emily Foster · Answer

Absolutely! Assigning a random number to a nonce in Content Security Policy (CSP) can help enhance security by preventing unauthorized scripts from running on your website. Let's break down how you can achieve this: 1. Understanding Nonces in CSP : Nonces are cryptographic tokens that help browsers ensure that a specific script or style is allowed to run. By assigning a nonce to scripts and styles, you can control which resources are executable, mitigating the risk of cross-site scripting (XSS) attacks. 2. Generating a Random Number : To assign a random value to your nonce, you can utilize server-side code to generate a unique value each time the page is loaded. This ensures that the nonce is unpredictable and changes on each request, strengthening the security of your CSP policy. 3. Implementing Random Nonces in CSP : - In your HTML file, you would typically have a script tag similar to: // Your script content here - To dynamically generate a nonce value, you can use a server-side language like C#, Java, or PHP to include a random number within the nonce attribute. - Here's a simplified example using C#: string randomNonce = Guid.NewGuid().ToString(); ViewBag.RandomNonce = randomNonce; // Assuming MVC model or ViewBag usage - Then in your HTML or Razor view, you can assign this random value to the nonce attribute: // Your script content here 4. Benefits of Random Nonces : - Enhanced Security : Random nonces add unpredictability, making it harder for attackers to bypass your CSP rules. - Dynamic Protection : With unique nonces per request, you can mitigate replay attacks and unauthorized script executions effectively. By following these steps and incorporating random nonces into your CSP policy, you can bolster the security of your DevExpress MVC application and prevent malicious scripts from running without proper authentication. Let me know if you need further clarification or more examples!