The Sign-up Sheets WordPress plugin before 2.2.13 does not escape some generated URLs, as well as the $_SERVER['REQUEST_URI'] parameter before outputting them back in attributes, which could lead to Reflected Cross-Site Scripting.
The Sign-up Sheets WordPress plugin before 1.0.14 does not not sanitise or validate the Sheet title when generating the CSV to export, which could lead to a CSV injection issue
The Sign-up Sheets WordPress plugin before 1.0.14 did not sanitise or escape some of its fields when creating a new sheet, allowing high privilege users to add JavaScript in them, leading to a Stored Cross-Site Scripting issue. The payloads will be triggered when viewing the 'All Sheets' page in the admin dashboard