Fixed broken link (#16757)

This content is no longer available on adobe and I found this site where the same original content is hosted.

files/en-us/web/http/headers/index.md

@@ -298,7 +298,7 @@ _Learn more about CORS [here](CORS)._
 - {{HTTPHeader("X-Frame-Options")}} (XFO)
   - : Indicates whether a browser should be allowed to render a page in a {{HTMLElement("frame")}}, {{HTMLElement("iframe")}}, {{HTMLElement("embed")}} or {{HTMLElement("object")}}.
 - {{HTTPHeader("X-Permitted-Cross-Domain-Policies")}}
-  - : Specifies if a cross-domain policy file (`crossdomain.xml`) is allowed. The file may define a policy to grant clients, such as Adobe's Flash Player (now obsolete), Adobe Acrobat, Microsoft Silverlight (now obsolete), or Apache Flex, permission to handle data across domains that would otherwise be restricted due to the [Same-Origin Policy](/en-US/docs/Web/Security/Same-origin_policy). See the [Cross-domain Policy File Specification](https://www.adobe.com/devnet/articles/crossdomain_policy_file_spec.html) for more information.
+  - : Specifies if a cross-domain policy file (`crossdomain.xml`) is allowed. The file may define a policy to grant clients, such as Adobe's Flash Player (now obsolete), Adobe Acrobat, Microsoft Silverlight (now obsolete), or Apache Flex, permission to handle data across domains that would otherwise be restricted due to the [Same-Origin Policy](/en-US/docs/Web/Security/Same-origin_policy). See the [Cross-domain Policy File Specification](https://hubsadda.com/cross-domain-policy-file-specification/) for more information.
 - {{HTTPHeader("X-Powered-By")}}
   - : May be set by hosting environments or other frameworks and contains information about them while not providing any usefulness to the application or its visitors. Unset this header to avoid exposing potential vulnerabilities.
 - {{HTTPHeader("X-XSS-Protection")}}