Admidio is an open-source user management solution. Prior to 5.0.6, in modules/events/eventsfunction.php, the event participation logic allows any user who can participate in an event to register OTHER users by manipulating the useruuid GET parameter. The condition uses || (OR), meaning if possibleToParticipate() returns true (event is open for participation), ANY user - not just leaders - can specify a different useruuid and register/cancel participation for that user. The code then operates on $user->getValue('usrid') (the target user from user_uuid) rather than the current user. This vulnerability is fixed in 5.0.6.
{
"cwe_ids": [
"CWE-639"
],
"cna_assigner": "GitHub_M",
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/30xxx/CVE-2026-30927.json"
}