CVE-2026-24513 concerns a security flaw in the Kubernetes ingress-nginx controller involving the auth-url Ingress annotation, which is designed to enforce authentication on incoming requests. The vulnerability arises when ingress-nginx is configured with a default custom-errors backend that handles HTTP 401 (Unauthorized) or 403 (Forbidden) errors, but this backend is defective in that it does not respect the X-Code HTTP header. The X-Code header is used internally by ingress-nginx to determine the response code from the authentication backend. If the custom-errors backend mishandles this header, ingress-nginx may incorrectly allow access to resources protected by auth-url, effectively bypassing authentication. This flaw is categorized under CWE-754, indicating improper checks for unusual or exceptional conditions. Exploitation requires an administrator to have deliberately configured ingress-nginx with a broken external custom-errors backend, as the default built-in backend functions correctly. The CVSS v3.1 score is 3.1 (low), reflecting the requirement for a high attack complexity and limited impact confined to confidentiality. No integrity or availability impacts are noted, and no user interaction is required. No known exploits have been reported in the wild. This vulnerability highlights the risks of relying on external components for critical security functions without thorough validation.

For European organizations, the primary impact of CVE-2026-24513 is a potential confidentiality breach where unauthorized users might gain access to resources protected by ingress-nginx's auth-url annotation if a misconfigured custom-errors backend is in use. Since the vulnerability does not affect integrity or availability, the risk is limited to unauthorized data exposure. Organizations using ingress-nginx with custom error backends that handle 401 or 403 errors are at risk if those backends fail to correctly process the X-Code HTTP header. This could lead to unauthorized access to internal services or APIs exposed via Kubernetes Ingress, potentially exposing sensitive information or internal application endpoints. However, the requirement for a specific misconfiguration and the absence of known exploits reduce the likelihood of widespread impact. Nonetheless, given the widespread adoption of Kubernetes and ingress-nginx in European enterprises, especially in sectors like finance, healthcare, and government, even limited unauthorized access could have regulatory and reputational consequences under GDPR and other data protection frameworks.

European organizations should audit their ingress-nginx configurations to verify whether a custom-errors backend is used for handling HTTP 401 or 403 errors. If so, they must ensure that the backend correctly respects the X-Code HTTP header to prevent authentication bypass. The safest approach is to use the built-in custom-errors backend provided by ingress-nginx, which is confirmed to handle the header correctly. Administrators should avoid deploying external or custom error backends unless thoroughly tested for compliance with ingress-nginx's expected behavior. Additionally, organizations should implement strict configuration management and change control processes to prevent accidental deployment of defective backends. Monitoring ingress-nginx logs for unexpected access patterns or authentication bypass attempts can help detect exploitation attempts. Finally, keeping ingress-nginx updated with the latest patches and security advisories is essential, even though no patch links are currently provided for this CVE.