CVE-2026-24513 in ingress-nginx
Summary
by MITRE • 02/04/2026
A security issue was discovered in ingress-nginx where the protection afforded by the `auth-url` Ingress annotation may not be effective in the presence of a specific misconfiguration.
If the ingress-nginx controller is configured with a default custom-errors configuration that includes HTTP errors 401 or 403, and if the configured default custom-errors backend is defective and fails to respect the X-Code HTTP header, then an Ingress with the `auth-url` annotation may be accessed even when authentication fails.
Note that the built-in custom-errors backend works correctly. To trigger this issue requires an administrator to specifically configure ingress-nginx with a broken external component.
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Analysis
by VulDB Data Team • 02/18/2026
This vulnerability resides within the ingress-nginx controller implementation where the authentication mechanism fails to properly enforce access controls due to a specific configuration interaction. The flaw manifests when administrators configure ingress-nginx with custom error handling that includes HTTP status codes 401 and 403, combined with an external backend component that does not properly respect the X-Code HTTP header. This creates a scenario where authentication failures do not result in proper access denial, allowing unauthorized users to bypass authentication checks. The vulnerability represents a failure in the principle of least privilege and demonstrates how misconfigured security components can undermine the intended protection mechanisms. From a cybersecurity perspective, this issue aligns with CWE-284 Access Control Issues, specifically concerning improper access control enforcement when authentication fails.
The technical execution of this vulnerability requires a specific combination of misconfigurations that must be present simultaneously for the flaw to manifest. The ingress-nginx controller's default behavior correctly handles authentication through the `auth-url` annotation, but when paired with a custom error backend that fails to process the X-Code header properly, the authentication failure does not result in the expected access denial. This creates an authentication bypass where users can access protected resources even when their authentication attempts fail. The root cause lies in the improper handling of HTTP headers within the custom error backend component, which should forward the X-Code header to properly signal authentication failures to the client. The vulnerability operates at the application layer and demonstrates how HTTP header processing can affect security decisions in reverse proxy implementations.
The operational impact of this vulnerability extends beyond simple access control bypass to potentially expose sensitive resources to unauthorized access. When authentication fails due to the misconfigured error handling, legitimate authentication failures do not result in proper access denial, creating a persistent security gap. This could allow attackers to gain access to protected applications, data, or services that should only be accessible to authenticated users. The vulnerability affects organizations that have customized their ingress-nginx error handling configurations and may not be immediately apparent during routine security assessments, as the flaw only manifests when specific conditions are met. This creates a stealthy security risk that could persist undetected for extended periods.
Mitigation strategies for this vulnerability require administrators to ensure proper configuration of custom error backends within their ingress-nginx deployments. The primary recommendation is to verify that any custom error handling components properly respect and process the X-Code HTTP header, ensuring that authentication failures result in appropriate access denial. Organizations should also consider implementing monitoring to detect when authentication failures are not properly enforced, potentially through log analysis or security information and event management systems. Additionally, administrators should avoid using custom error backends that do not properly handle HTTP status code propagation, and should validate that their error handling components are compatible with ingress-nginx's authentication mechanisms. This aligns with ATT&CK technique T1566 Credential Access through the potential for bypassing authentication controls, and follows security best practices for maintaining proper access control enforcement in reverse proxy configurations. The vulnerability highlights the importance of thorough testing when implementing custom security components and the need for proper header handling in HTTP-based security systems.