Server-Side Request Forgery (SSRF)
Plone through 5.2.4 allows remote authenticated managers to conduct SSRF attacks via an event ical URL, to read one line of a file. This issue was partially fixed in plone.app.event 3.2.10 and fully fixed in hotfix 20210518 (Plone version 5.2.5 includes the hotfix)
CWE-918 - Server-Side Request Forgery (SSRF)
Server-side request forgery (SSRF) is a weakness that allows an attacker to send an arbitrary request, making it appear that the request was sent by the server. This request may bypass a firewall that would normally prevent direct access to the URL. The impact of this vulnerability can vary from unauthorized access to files and sensitive information to remote code execution.