Content Security Policy with Next.js: Leveling Up your Website's Security
From Author:
In this talk, we'll explore the powerful security feature of Content Security Policy (CSP) and how it can be implemented in Next.js to bolster your website's defenses against common web attacks like Cross-Site Scripting (XSS) and data injection. We'll cover the basics of CSP, its benefits, and best practices for implementing it in Next.js.
Additionally, we'll share some tools to evaluate and test your policy. By the end of this talk, you'll have a solid understanding of how to level up your website's security with CSP and protect your users from the ever-present threats of the modern web.
This talk has been presented at React Summit US 2023, check out the latest edition of this React Conference.
FAQ
Yes, a Content Security Policy can be tailored to be environment-specific. For instance, in a development environment, a CSP can be more relaxed to facilitate testing, while in production, it can be made stricter to provide enhanced security against attacks.
Examples of policy directives in a CSP include specifying default sources of content, such as limiting sources to your own domain, and adding exceptions, like allowing Google web fonts to be downloaded. These directives help control where content can be loaded from, enhancing security.
To validate a CSP for a Next.js application, you can use tools like Google's CSP Evaluator or Mozilla Observatory. These tools analyze the CSP and provide reports on potential improvements or issues, helping ensure the policy effectively secures the application.
A 'nonce' is a one-time token used in a CSP to allow specific inline scripts or styles to execute while maintaining overall policy compliance. This is useful when you need to run inline scripts safely, as each script must include the unique nonce value to execute.
In a Next.js app, a CSP prevents unauthorized content by enforcing rules that restrict external content sources. For example, if a CSP only allows content from the app's own domain, any attempt to load an image from a different domain would be blocked unless explicitly allowed in the CSP.
A Content Security Policy (CSP) is a security layer that helps shield applications from threats like cross-site scripting (XSS) and data injection attacks by restricting browser functionality. It defines a list of policy directives that limit what the browser is allowed to execute, enhancing the security of web applications.
You can find examples and detailed documentation on implementing Content Security Policies in Next.js on the official Next.js documentation website. Additionally, sample applications implementing CSP can often be found on repositories like GitHub.
To implement a Content Security Policy in a Next.js application, you can add a CSP directly in the HTML using a meta tag in the head section or more securely through HTTP headers. The Next.js documentation provides detailed options on how to add different headers, including CSP, to your application configuration.
Video Transcription
1. Introduction to Content Security Policy
I'm Lucas Estevão, Principal UI Engineer and Technical Manager at Avenue Code, a consultancy through which I've been helping companies like Toys R Us, Wal-Mart and even the iconic Apple to build better software. I am really excited to talk to you about Content Security Policy with Next.js and how you can level up your website security. A CSP or a content security policy is a security layer that helps to shield applications from like cross-type scripting, XSS or data injection attacks, and it does it by restricting the browser functionality.
Hi everyone. Thanks for having me at the React Summit US 2023. I'm Lucas Estevão, Principal UI Engineer and Technical Manager at Avenue Code, a consultancy through which I've been helping companies like Toys R Us, Wal-Mart and even the iconic Apple to build better software. I also host a podcast about career in tech for Portuguese speakers, so if you're curious, check it out on the major streaming platforms. You just need to search for Códigos de Carreira.
I am really excited to talk to you about Content Security Policy with Next.js and how you can level up your website security. I want to start answering why should I care about a content security policy? And to keep it short, your browser is not 100% safe. Neither is React or Next.js or whatever framework that you might be using. Although browsers do have built-in security features like single origin policy and course, we can't take it for granted. The libraries and frameworks like React or Next.js, again, they do a pretty decent job sanitizing the code and providing with features to close the security gaps, but that's not enough. If a code like this is injected in your website, your browser or React default features can't prevent this from being executed. That's when a CSP comes handy.
A CSP or a content security policy is a security layer that helps to shield applications from like cross-type scripting, XSS or data injection attacks, and it does it by restricting the browser functionality. A CSP is composed by a list of policy directives. The browser will be limited to allow only what the policy defines. Here are examples of policy directives, where I'm defining that the default sources of content should come from my domain and I'm adding an exception for fonts because I want to allow Google web fonts to be downloaded. Now let's see how we can implement that in an XJS app. Let's go hands-on now.
2. Adding Content Security Policy
This is an XJS application. We want to add the CSP to the page. The easiest way is by adding it to the head tag using a meta tag. Let's try adding headers instead. We'll add a simple content security policy to see it working on the headers. Next, we'll try using a middleware to add a content security policy. Create a new file called middleware.ts on the root of our app and refer to the documentation for more details.
Okay, so this is an XJS application, just a template I created using NPX. The first thing we want to try to do is to add the CSP to the page. And the easiest way to do it is adding this on the head tag using a meta tag.
So let's go to the application and see that the image is not being displayed here. And the image is not being displayed because it comes from a different domain. It comes from React Summit. And my directive it's enforcing that the content should come by default from my own domain. The image shouldn't show up, but let's remove this from here. That's not the best way to add a content security policy.
Let's try doing it adding headers. So if you go to the documentation, you see how to add headers to your Next.js application, and you see a bunch of options to add different headers, including the content security policy. So I prepared something here. I picked a few of the security headers. I'm gonna add them to our Next.js config app. And I'm going to add the headers as well. And again, this is all available on the docs. I'm gonna save this, and let's go to step number two.
What we wanna do here is just to add a simple content security policy to actually see it working on the headers. So I'm gonna do this and add the content security policy to my header. And I wanna see this happening in action. It's reloading. I'm gonna reload this page. Just to make sure, I'm gonna go to the network tab. Let's check it out. Open this, you can see the content security policy is there exactly the way we set it. The image is still not showing up. Let's go to step number three and actually try to use it to add a content security policy using a middleware. And for that, we're gonna create a new file on the root of our app. So new file, actually not here, but on the root, new file middleware.ts, let me move this to here. And if you go to the documentation again, you can see everything about how work with the middlewares.
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