CVE-2026-30927: Admidio: Event participation IDOR - non-leaders can register other users for events via user_uuid parameter

Severity: medium (CVSS 5.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-03-10 · updated 2026-06-17
Weakness: CWE-639

Description

Admidio is an open-source user management solution. Prior to 5.0.6, in modules/events/events_function.php, the event participation logic allows any user who can participate in an event to register OTHER users by manipulating the user_uuid 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 user_uuid and register/cancel participation for that user. The code then operates on $user->getValue('usr_id') (the target user from user_uuid) rather than the current user. This vulnerability is fixed in 5.0.6.

Affected products

admidio: before 5.0.6 — fixed in 5.0.6

How to fix

Upgrade to a fixed version: admidio 5.0.6. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2026-30927 or the next vulnerability affects your stack