Description

The Default session expiration time feature when submitted HTML/JS tags executes the code in the login page.

Proof of Concept

Login to Teampass and go to Settings => Options. (http://127.0.0.1/index.php?page=options)
In theDefault session expiration time input field insert an XSS payload "><svg/onload=alert(document.cookie)>. Save the settings.

On a different browser, open the login page. The XSS payload executes.