CVE-2026-41662: Admidio Auth Bypass Vulnerability

CVE-2026-41662 Overview

CVE-2026-41662 affects Admidio, an open-source user management solution used by organizations to manage members, groups, and roles. The vulnerability exists in the Role::stopMembership() function, which fails to verify whether removing a user from the administrator role would leave the system without any administrators. Versions prior to 5.0.9 are affected. An authenticated administrator can remove the last remaining administrator account, resulting in complete loss of administrative access to the application. The deprecated Membership::stopMembership() method retained the safety check, but the active code path bypasses it.

Critical Impact

Authenticated administrators can lock the entire Admidio instance out of administrative access by removing the last remaining administrator, requiring database-level recovery.

Affected Products

• Admidio versions prior to 5.0.9
• Admidio open-source user management solution
• Self-hosted Admidio deployments using the affected role management code path

Discovery Timeline

• 2026-05-07 - CVE-2026-41662 published to NVD
• 2026-05-07 - Last updated in NVD database

Technical Details for CVE-2026-41662

Vulnerability Analysis

The vulnerability is classified as [CWE-754]: Improper Check for Unusual or Exceptional Conditions. The Role::stopMembership() function in Admidio handles the removal of users from roles, including the privileged administrator role. The function lacks a precondition check verifying that at least one administrator remains after the removal completes.

Admidio previously implemented this check in the Membership::stopMembership() method, which is now deprecated. The current code path no longer invokes the deprecated method or replicates its validation logic. As a result, role removal operations against the administrator role proceed without enforcing the minimum administrator constraint.

The issue does not require a race condition. Sequential removal requests by an authenticated administrator produce the same outcome as concurrent requests. After the last administrator is removed, no user can perform administrative actions through the application interface.

Root Cause

The root cause is missing business logic validation in Role::stopMembership(). The function does not query the count of remaining members in the administrator role before completing the removal. The safety check that existed in the deprecated Membership::stopMembership() method was not migrated to the replacement code path.

Attack Vector

Exploitation requires authentication as an existing administrator and user interaction through the role management interface. An administrator submits a request to remove another administrator from the administrator role. When that user is the last remaining administrator other than the requester, or when removals are sequenced to eliminate all administrators, the application accepts the operation without warning. The result is administrative lockout of the Admidio instance.

No verified exploit code is publicly available. See the GitHub Security Advisory GHSA-c7xm-r6vj-8vg6 for vendor-published technical details.

Detection Methods for CVE-2026-41662

Indicators of Compromise

• Audit log entries showing membership removal events targeting the administrator role in close succession
• Sudden absence of users assigned to the administrator role in the Admidio database
• Failed administrative login attempts following role membership changes
• Database adm_members table entries with end dates set on all administrator role assignments

Detection Strategies

• Monitor Admidio application logs for Role::stopMembership() invocations against the administrator role identifier
• Query the database periodically to count active administrator role memberships and alert when the count reaches one
• Review web server access logs for sequential POST requests to role membership endpoints from a single session

Monitoring Recommendations

• Enable verbose audit logging in Admidio for all role membership changes
• Forward Admidio logs to a centralized logging platform for correlation and alerting
• Establish a baseline count of administrator accounts and alert on deviations
• Implement file integrity monitoring on Admidio PHP source files to detect unauthorized modifications

How to Mitigate CVE-2026-41662

Immediate Actions Required

• Upgrade Admidio to version 5.0.9 or later, which contains the patched validation logic
• Audit current administrator role membership and ensure at least two trusted administrator accounts exist
• Review recent role membership changes for unauthorized removals
• Restrict administrator account provisioning to a small set of trusted users

Patch Information

The vendor patched this issue in Admidio version 5.0.9. The fix restores the minimum administrator validation in the active Role::stopMembership() code path. Refer to the GitHub Release v5.0.9 and the GitHub Security Advisory GHSA-c7xm-r6vj-8vg6 for release notes and remediation guidance.

Workarounds

• Maintain a database-level backup administrator account that bypasses the application logic for emergency recovery
• Limit the number of users granted administrator privileges to reduce exposure to malicious or accidental removals
• Apply application-layer access controls or web application firewall rules to restrict access to role management endpoints
• Take regular database backups to enable rapid restoration if administrative lockout occurs