Created attachment 419048 [details]
Example html document

Overview:
If an iframe has the sandbox attribute without allow-script, then Safari web extension event listeners won't get  called in the iframe.

This is contrary to Google Chrome, which does allow extension event listeners in a sandbox iframe. Moreover, Content-Security-Policy script-src 'none' also still allows extension event listeners. So iframe sandbox should only prevent web page script, not extension script.


Steps to Reproduce:
1. Put the attached "index.html" document in /Users/Shared (to avoid Mac TCC issues)
2. cd /Users/Shared
3. /usr/bin/python -m SimpleHTTPServer 8000
4. Build and run the attached sample Xcode project "SandboxTest"
5. Open Safari
6. Select "Allow Unsigned Extensions" from the Develop menu.
7. Open Safari Preferences Extensions pane.
8. Enable the SandboxTest extension.
9. Select "Always Allow on Every Website..."
10. Open http://localhost:8000
11. Open the web inspector console
12. Click inside the sandbox iframe

Actual Results:
[Error] Blocked script execution in 'https://example.org/' because the document's frame is sandboxed and the 'allow-scripts' permission is not set.

Expected Results:
[Log] SandboxTest mousedown:  – "H1" (content.js, line 7)

Additional Information:
This bug also affects Safari app extensions and affects Safari 14 on Catalina and Mojave on Intel Macs.