The plugin does not sanitise and escape some parameters, which could allow high privilege users such as admin to perform Stored Cross-Site Scripting attacks even when the unfiltered_html capability is disallowed (for example in multisite setup)
Proof of Concept
1. Navigate toward the GYG Ticketing and GYG Ticketing > Link builder.
2. Enter the XSS payload: " style=animation-name:rotation onanimationstart=alert(/XSS/)//
3. Go to Link builder and click on Generate links to trigger the XSS