A stored cross-site scripting (XSS) vulnerability exists ArcGIS HUB and ArcGIS Enterprise Sites which allows an authenticated user with the ability to create or edit a site to add and store an XSS payload. If this stored XSS payload is triggered by any user attacker supplied JavaScript may execute in the victim's browser.
https://www.esri.com/arcgis-blog/products/trust-arcgis/administration/2925891-2