Issue Summary

User Macro with iFrame in it causing Page Preview to load indefinitely

Steps to Reproduce

1. Create a User Macro with minimum content that simply just renders what's in it. For Example:
   Example User Macro

   ## Body processing: Rendered
   ## @noparams
   
                     $body
   

2. Enable HTML Macro
3. Create a new page
4. Insert the User Macro above with a HTML Macro that contains an <iframe> tag to any website
   Example Storage Format

   <ac:structured-macro ac:macro-id="3f1c5ba7-6915-46dc-b2ea-cb5707e23f2a" ac:name="brokenpreview" ac:schema-version="1">
     <ac:parameter ac:name="atlassian-macro-output-type">INLINE</ac:parameter>
     <ac:rich-text-body>
   
       <ac:structured-macro ac:macro-id="9405e293-52c1-4bc5-b48c-ab065324895f" ac:name="html" ac:schema-version="1">
         <ac:plain-text-body><![CDATA[<iframe src="https://google.com" </iframe>]]></ac:plain-text-body>
       </ac:structured-macro>
   
     </ac:rich-text-body>
   </ac:structured-macro>
   

5. Click the "Preview" button

Expected Results

Page Preview will show how the page supposed to look like

Actual Results

Page Preview loads indefinitely

Note

• using HTML for Confluence third-party macro will result in the same issue
• using <img> tag will not hit into the issue

Workaround

Currently there is no known workaround for this behavior. A workaround will be added here when available