Subresource Integrity (SRI)

Definition

Subresource Integrity (SRI) is a security feature that enables browsers to verify that resources loaded from third-party sources have not been tampered with. It uses cryptographic hash functions to ensure that the content of a resource matches the expected hash value, thus providing a layer of trust and security in web applications. By implementing SRI, developers can prevent potential attacks where malicious code is injected into external scripts or stylesheets, enhancing both client-side and server-side security measures.

5 Must Know Facts For Your Next Test

1. SRI uses a 'hash' attribute in the HTML <script> and <link> tags to ensure the integrity of the loaded resource.
2. If the fetched resource does not match the specified hash, the browser will block its execution, preventing potentially harmful code from running.
3. SRI supports multiple hash algorithms, such as SHA-256, SHA-384, and SHA-512, allowing flexibility in choosing the level of security.
4. By leveraging SRI, developers can improve the overall security posture of web applications, particularly when using popular CDNs for loading scripts and styles.
5. The implementation of SRI is a best practice for modern web development, particularly in an environment where third-party resources are widely used.

Review Questions

• How does Subresource Integrity enhance the security of web applications?
  • Subresource Integrity enhances the security of web applications by allowing browsers to verify that external resources have not been altered. By using cryptographic hashes, developers specify expected content for scripts and styles. If any modification occurs, such as a malicious injection, the browser will prevent execution of the altered resource, effectively blocking potential threats and maintaining the integrity of the application.
• Discuss how SRI interacts with other security measures like Content Security Policy (CSP) in web applications.
  • SRI works alongside Content Security Policy (CSP) to create a more robust security framework for web applications. While SRI ensures that specific external resources remain unaltered by checking their hash values, CSP adds another layer by defining what sources are permitted to load content in the first place. Together, they help protect against various attacks, like Cross-Site Scripting (XSS), by validating both source origins and content integrity.
• Evaluate the impact of using Subresource Integrity on the performance and security of client-side web applications.
  • Using Subresource Integrity can have a positive impact on both performance and security in client-side web applications. Security-wise, it significantly reduces risks related to third-party resources being compromised or tampered with. Performance-wise, while there might be a minimal overhead in verifying hashes during resource loading, this is generally outweighed by enhanced user trust and reduced risk of injecting harmful scripts. Overall, implementing SRI supports a safer browsing experience without significant detriment to application performance.

Related terms

Content Security Policy (CSP): A security standard that helps prevent various attacks, such as Cross-Site Scripting (XSS) and data injection, by allowing developers to specify which sources of content are trusted.

Hash Function: A mathematical algorithm that transforms input data into a fixed-size string of characters, which is typically a digest that uniquely represents the input data.

Cross-Origin Resource Sharing (CORS): A security feature that allows or restricts resources requested from another domain outside the domain from which the resource was served, providing control over resource sharing.