Flash and Silverlight applications can no longer access ArcGIS Online content and services

Description

Esri is removing security policy files from ArcGIS Online that are used by the ArcGIS API for Flex on January 26, 2021, and for the ArcGIS API for Silverlight on October 12, 2021.

This means that after these dates, Flex and Silverlight apps can no longer access any content and/or services from ArcGIS Online. Furthermore, due to security vulnerabilities associated with running Flash, Adobe no longer supports Flash as of December 31, 2020, and is taking steps to block Flash-based apps from running altogether.

Cause

The ArcGIS API for Flex and the ArcGIS API for Silverlight were retired in June 2016. However, Esri kept these policy files accessible so developers who wanted to continue to use their deployed Flex and Silverlight apps could access content and services on ArcGIS Online:

• crossdomain.xml - for Flash-based clients
• clientaccesspolicy.xml - for Silverlight-based clients

These resources are being removed to protect customers from security vulnerabilities; in line with Adobe, Microsoft, and major browser vendors:

• Adobe will actively block Flash content from running in Flash Player beginning January 12, 2021.  
• According to Adobe, “Adobe does not intend to issue Flash Player updates or security patches.  Therefore, Adobe will continue to prompt users to uninstall Flash Player and strongly recommends that all users immediately uninstall Flash Player.”
• According to Microsoft, “Flash will be completely removed from all browsers by December 31, 2020, via Windows Update” (KB4577856).
• Google Chrome is removing Flash in January 2021.
• Firefox is removing Flash Jan 26, 2021.
• Safari disabled Flash in Sept 2020.
• Per Microsoft, Silverlight support will end 10/12/2021.

Solution or Workaround

If you have a Flex- or Silverlight-based app in production, Esri highly encourages migration to a JavaScript-based app using the ArcGIS API for JavaScript. The ArcGIS API for JavaScript is the focus of Esri’s web-based development and innovation, and far exceeds the capabilities of the older Flex and Silverlight APIs on many fronts.