The plugin does not sanitise or escape the Duplicate Post Suffix settings before outputting it, which could allow high privilege users to perform Stored Cross-Site Scripting attacks even when the unfiltered_html capability is disallowed.
The attempt to fix the issue in 4.4.2 is insufficient and still allows for XSS.
Proof of Concept
Put the following payload in the Duplicate Post Suffix setting of the plugin:
- v < 4.4.2: "><svg/onload=confirm(/XSS/)>
- v < 4.4.3: " style=animation-name:rotation onanimationstart=alert(/XSS/)//