CVE-2026-85594 in Traefik
Summary
by MITRE • 09/04/2026
Traefik versions from v3.7.1 fail to enforce crossProviderNamespaces restrictions on the traefik.ingress.kubernetes.io/service.middlewares Service annotation in the Kubernetes Ingress provider. A namespace-limited tenant excluded from the allowlist can attach an operator-owned middleware to its Service, and if that middleware injects backend credentials, recover them at a controlled backend.
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Analysis
by VulDB Data Team • 09/04/2026
The vulnerability identified in Traefik versions prior to v3.7.1 represents a critical failure in namespace isolation mechanisms within Kubernetes environments utilizing the Ingress provider. This flaw specifically impacts the enforcement of crossProviderNamespaces restrictions associated with the traefik.ingress.kubernetes.io/service.middlewares annotation. In multi-tenant or segmented Kubernetes clusters, administrators often rely on these annotations to restrict which middleware resources can be attached to services across different namespaces. The intended security model dictates that only specific, allowlisted providers should have access to certain middleware configurations, thereby preventing unauthorized entities from leveraging shared infrastructure components for malicious purposes. However, due to the implementation oversight in this version range, the validation logic fails to properly verify whether a tenant is explicitly excluded from the allowed list when attempting to reference an operator-owned middleware resource located in a different namespace.
This technical flaw allows a compromised or rogue user within a restricted namespace to bypass isolation boundaries and attach a middleware controlled by cluster operators to their own service definitions. The operational impact of this misconfiguration becomes severe when the targeted middleware is designed to inject backend credentials, such as authentication tokens, API keys, or session cookies, into outgoing requests. By exploiting this lack of enforcement, an attacker can route traffic through these operator-controlled middlewares, effectively gaining access to sensitive credential data that was intended for internal service-to-service communication only. Once attached, the middleware processes the request and injects the backend credentials, which are then transmitted over the network.
The consequence of this exploitation is a significant compromise of confidentiality and integrity within the cluster's microservices architecture. An attacker who controls a client application or can manipulate ingress rules in their namespace can configure it to use the compromised middleware. As requests pass through this pipeline, the injected credentials are exposed at a controlled backend endpoint that the attacker manages. This enables credential harvesting, unauthorized access to protected APIs, and potential lateral movement within the cluster if those credentials possess elevated privileges. The attack vector aligns with CWE-284 Improper Access Control, as it involves bypassing intended restrictions on resource access based on namespace boundaries. Furthermore, this behavior is consistent with ATT&CK technique T1530 Data from Cloud Storage Object or T1078 Valid Accounts if the injected credentials are used for further authentication, illustrating how configuration errors in service mesh and ingress controllers can lead to direct data exfiltration.
To mitigate this vulnerability, organizations must immediately upgrade Traefik to version v3.7.1 or later where these cross-namespace validation checks have been corrected. In addition to upgrading, administrators should review their Kubernetes RBAC policies to ensure that the ability to create and modify ingress resources is strictly limited to authorized users within each namespace. It is also advisable to implement network policies that restrict outbound traffic from pods unless explicitly permitted, adding a layer of defense-in-depth against credential exfiltration attempts. Regular auditing of middleware configurations and strict adherence to least-privilege principles for service account permissions will further reduce the risk surface associated with such configuration-based vulnerabilities in container orchestration platforms.