IIS · December 18, 2023

IIS Security Tip: Implement Subresource Integrity (SRI) for external scripts and styles

IIS Security Tip: Implement Subresource Integrity (SRI) for external scripts and styles

When it comes to website security, it is crucial to take every possible measure to protect your website and its visitors from potential threats. One often overlooked aspect of security is the integrity of external scripts and stylesheets that are loaded on your website. In this article, we will explore the concept of Subresource Integrity (SRI) and how it can enhance the security of your IIS-hosted website.

What is Subresource Integrity (SRI)?

Subresource Integrity (SRI) is a security feature that allows you to ensure the integrity and authenticity of external resources, such as scripts and stylesheets, that are loaded on your website. It works by generating a cryptographic hash of the resource file and comparing it with the hash provided in the HTML code. If the hashes match, it means that the resource has not been tampered with and can be safely executed.

By implementing SRI, you can protect your website from various attacks, including:

  • Man-in-the-Middle (MitM) Attacks: Attackers intercept the communication between the server and the client and modify the external resource to inject malicious code.
  • Content Delivery Network (CDN) Compromises: CDNs can be compromised, leading to the delivery of malicious scripts or stylesheets to your website.
  • Third-Party Script Vulnerabilities: External scripts may contain vulnerabilities that can be exploited by attackers to compromise your website.

Implementing SRI in IIS

Implementing SRI in IIS is a straightforward process. Here's a step-by-step guide:

  1. Generate the Integrity Hash: Use a tool like the srihash.org website or a command-line tool to generate the integrity hash for your external resource. This hash will be used in the HTML code to verify the integrity of the resource.
  2. Add the Integrity Attribute: In your HTML code, add the integrity attribute to the <script> or <link> tag that references the external resource. Set the value of the attribute to the generated integrity hash.
  3. Add the Crossorigin Attribute: To ensure that the browser performs the integrity check, add the crossorigin attribute to the <script> or <link> tag. Set the value of the attribute to "anonymous".

By following these steps, you can ensure that the external resources loaded on your website are verified for integrity before execution, providing an additional layer of security.

Conclusion

Implementing Subresource Integrity (SRI) for external scripts and stylesheets is a simple yet effective way to enhance the security of your IIS-hosted website. By verifying the integrity of these resources, you can protect your website and its visitors from potential attacks and compromises.

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