Update the WordPress Spiffy Calendar plugin to the latest available version (at least 4.9.1).
thiennv discovered and reported this Cross Site Request Forgery (CSRF) vulnerability in WordPress Spiffy Calendar Plugin. This could allow a malicious actor to force higher privileged users to execute unwanted actions under their current authentication. For example a password change which will then allow the malicious actor to login into the admin account. This vulnerability has been fixed in version 4.9.1.
Authenticated Reflected CrossSite Scripting (XSS) vulnerability
Admin+ Persistent CrossSite Scripting (XSS) vulnerability
Multiple Authenticated Reflected CrossSite Scripting (XSS) vulnerabilities
Edit/Delete event via IDOR vulnerability