Cross-Domain JavaScript Inclusion via Third-Party CDN/ CWE: 829 – Inclusion of Functionality from Untrusted Control Sphere/ WASC: 15 – Application Misconfiguration

[zoro1081]

Cross-Domain JavaScript Inclusion via Third-Party CDN/ CWE: 829 – Inclusion of Functionality from Untrusted Control Sphere/ WASC: 15 – Application Misconfiguration

Summary

The application loads a JavaScript file from a third-party domain (cdn.jsdelivr.net).
If the external source is compromised, altered, or maliciously replaced, it could result in arbitrary JavaScript execution within the context of blog.cerebrum.com. This represents a supply-chain risk and weakens the application’s trust boundary.

The page includes an externally hosted JavaScript resource:

https://cdn.jsdelivr.net/ghost/portal@~2.56/umd/portal.min.js

When a browser loads JavaScript from a third-party domain, that script executes with the same privileges as first-party code. Any compromise of the CDN, package, or dependency chain would directly impact users visiting the site.

This risk is elevated when:

• Subresource Integrity (SRI) is not enforced
• CSP script source restrictions are weak or missing
• Version ranges (e.g. ~2.56) are used instead of pinned hashes

Affected Asset

URL: https://blog.cerebrum.com/

Proof of Concept

HTTP Request

GET / HTTP/1.1
Host: blog.cerebrum.com
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64)
Accept: text/html
Cache-Control: no-cache
Pragma: no-cache
Referer: https://www.cerebrum.com/

HTTP Response

<script defer src="https://cdn.jsdelivr.net/ghost/portal@~2.56/umd/portal.min.js" data-i18n="true" data-ghost="https://blog.cerebrum.com/" data-key="9695f9c9c4871b0e3495e9464c" data-api="https://blog.cerebrum.com/ghost/api/content/" data-locale="en" crossorigin="anonymous"> </script>

Observe here that JavaScript is loaded from an external domain without integrity verification.

Security Impact

If the third-party script is compromised, an attacker could:

• Execute arbitrary JavaScript in user browsers
• Steal session tokens, cookies, or local storage data
• Inject malicious UI elements or phishing forms
• Modify page content or behavior
• Track users or exfiltrate sensitive information

This issue represents a client-side supply-chain attack vector.

Attack Scenario

• Attacker compromises the third-party CDN or package
• Malicious JavaScript is served to blog.cerebrum.com
• Visitors load and execute the modified script automatically
• Attacker gains execution in the site’s origin context

Root Cause

• Reliance on third-party JavaScript hosted outside the application’s domain
• No Subresource Integrity (SRI) hash enforced
• External script execution trusted implicitly

Recommendation

• Reduce exposure to third-party JavaScript risks by implementing the following controls:

Use Subresource Integrity (SRI)

<script src="https://cdn.jsdelivr.net/ghost/portal@~2.56/umd/portal.min.js" integrity="sha384-" crossorigin="anonymous"> </script>

Pin Exact Versions Avoid version ranges (~2.56) and use fixed versions to prevent unexpected updates.

Enforce CSP Script Restrictions Content-Security-Policy: script-src 'self' https://cdn.jsdelivr.net;

Self-Host Critical Scripts Host critical JavaScript assets locally when feasible.

References

• OWASP: Third-Party JavaScript Risks https://owasp.org/www-community/attacks/Third-party_Javascript
• MDN: Subresource Integrity https://developer.mozilla.org/en-US/docs/Web/Security/Subresource_Integrity
• OWASP Supply Chain Attacks https://owasp.org/www-project-top-ten/2017/A9_2017-Using_Components_with_Known_Vulnerabilities