Admidio is an open-source user management solution. In versions 5.0.6 and below, the save_membership action in modules/profile/profile_function.php saves changes to a member's role membership start and end dates but does not validate the CSRF token. The handler checks stop_membership and remove_former_membership against the CSRF token but omits save_membership from that check. Because membership UUIDs appear in the HTML source visible to authenticated users, an attacker can embed a crafted POST form on any external page and trick a role leader into submitting it, silently altering membership dates for any member of roles the victim leads. A role leader's session can be silently exploited via CSRF to manipulate any member's membership dates, terminating access by backdating, covertly extending unauthorized access, or revoking role-restricted features, all without confirmation, notification, or administrative approval. This issue has been fixed in version 5.0.7.