Content Security Policy (CSP) defines trusted sources for web resources like scripts and images to block malicious code and improve site protection.
What Is Content Security Policy (CSP)?
Content Security Policy (CSP) is a standardized security mechanism that informs browsers which content sources a website may load and run. CSP works through an HTTP response header (or meta tag) listing permitted origins for scripts, CSS, images, fonts and more. It limits execution of untrusted code, making it harder for attackers to inject malicious scripts or perform code injection attacks.
A properly configured CSP helps defend your site from Cross-Site Scripting (XSS), clickjacking, data injection, and other threats by preventing browsers from loading unauthorized resources.
It uses a "whitelist" approach so that only specified domains and protocols are allowed. Resources outside these rules are blocked by the browser engine.
Key Features of Content Security Policy (CSP)
1.Fine-Grained Source Whitelisting
CSP allows precise control over where different types of resources can originate. Instead of trusting all external content, developers can specify exact domains for scripts, stylesheets, images, fonts, and media. This granular control reduces the attack surface while keeping essential third-party services functional.
2.Strong Protection Against Inline Script Abuse
By default, CSP blocks inline JavaScript and dynamic code execution methods such as eval(). Only explicitly approved scripts—defined via hashes or nonces—are allowed to run. This feature is especially effective against Cross-Site Scripting (XSS) attacks that rely on injected inline code.
3.Directive-Based Resource Management
CSP uses clear directives like script-src, style-src, img-src, and connect-src to manage each resource type independently. This structure helps teams apply strict rules where risk is highest, such as JavaScript execution, while keeping flexibility for lower-risk assets.
4.Report-Only Mode for Safe Deployment
CSP supports a Content-Security-Policy-Report-Only mode, which logs violations without blocking content. This allows developers to monitor real-world behavior, detect misconfigurations, and refine policies before enforcing them in production.
5.Mitigation of Data Injection Attacks
Beyond XSS, CSP helps prevent malicious data injection through unauthorized frames, objects, or connections. Blocking unknown endpoints limits the ability of attackers to exfiltrate data or load harmful external resources.
6.Broad Browser Compatibility
Most modern browsers fully support CSP, making it a reliable, standardized security layer. Even when partial support exists, CSP still strengthens the browser's default same-origin protections without breaking compatibility.
Use Cases of Content Security Policy (CSP)
1.Web Applications and Dashboards
Complex web apps often load dynamic scripts and APIs. CSP helps ensure that only approved services and internal logic execute, reducing the risk of injected code compromising user sessions or sensitive data.
2.E-commerce Checkout and Payment Pages
Checkout pages handle high-value user data. A strict CSP limits third-party scripts and unauthorized connections, protecting customers from form-jacking attacks and credential theft.
3.Content-Heavy and Media Platforms
Sites that rely on external images, videos, or embedded content benefit from CSP by defining trusted media sources. This prevents malicious embeds while maintaining performance and content delivery flexibility.
4.Enterprise Security and Compliance
CSP supports security best practices recommended by frameworks like OWASP. Organizations can use it as part of a layered defense strategy to meet internal security standards and external compliance requirements.
5.Multi-Account and Browser Environment Management
When managing multiple browser profiles or isolated environments, CSP helps prevent unauthorized script execution and cross-context contamination, reinforcing consistent security behavior across sessions.
FAQ
1.What is CSP Content-Security-Policy?
A CSP is an HTTP header or meta tag that defines approved content sources for a website to prevent code injection and security threats.
2.What is an example of a CSP?
A simple CSP example:
Content-Security-Policy: default-src 'self'; script-src 'self' https://trustedcdn.example.com; img-src 'self' data:;
This allows scripts only from your own domain and a trusted CDN, and images either from your domain or inline data URIs.
3.What is the concept of CSP?
The concept is to use a whitelist model so the browser loads only trusted content. This prevents unauthorized resources and malicious scripts from executing.
4.How to fix Content-Security-Policy CSP header not set?
Ensure your server adds the Content-Security-Policy header in HTTP responses. For Apache/Nginx, configure your server rules; for frameworks, set header middleware. Testing in report-only mode helps identify policy issues before enforcing.
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