Steps to reproduce:
Make a template Template:TextXSS:
<noinclude>{{#cargo_declare: _table=TestXSS |field1=String (mandatory) }} </noinclude><includeonly> Field1 is {{{field1}}} {{#cargo_store: _table=TestXSS |field1={{{field1}}} }} </includeonly>
And create the table.
Make a page Item:
{{TestXSS|field1=<script>alert(1)</script>}}
Go to Special:CargoQuery. Put table as TestXSS, field as TestXSS.field1. Keep format as (default). Hit submit, notice the popup box