Cross-site request forgery (CSRF) vulnerability in the mycalendar plugin before 0.13 for Serendipity allows remote attackers to perform actions as blog administrators, which can be leveraged to conduct cross-site scripting (XSS) attacks on the blog page.
Cross-Site Request Forgery The web application does not, or cannot, sufficiently verify whether a request was intentionally provided by the user who sent the request, which could have originated from an unauthorized actor.