Envoy Gateway custom backendRef cross-namespace ReferenceGrant bypass

MITTEL 6.4CVE-2026-53718 · BIT-envoy-gateway-2026-53718 · GHSA-fcrp-7gc2-93g7 · Published 14/09/2026 · updated 25/09/2026

Kurz gesagt

CVE-2026-53718 ist eine Schwachstelle (MITTEL (CVSS 6.4)) in github.com/envoyproxy/gateway.
Wahrscheinlichkeit einer Ausnutzung in den nächsten 30 Tagen (EPSS): 0.41%, höher als bei 35.6% aller Schwachstellen.
Abhilfe: auf 1.8.1, 1.7.4 oder neuer aktualisieren.

Package	Affected versions	Patched versions
github.com/envoyproxy/gateway Go	`≥ 1.8.0-rc.0, < 1.8.1< 1.7.4`	`1.8.11.7.4`

Description

Impact

Envoy Gateway accepts extension-managed custom backendRefs from an HTTPRoute to a backend resource in another namespace without requiring a matching Gateway API ReferenceGrant in the target namespace. This breaks the Gateway API cross-namespace consent model: the namespace that owns the referenced backend resource does not need to opt in with a ReferenceGrant before another namespace’s HTTPRoute can use that resource.

Patches

1.7.4 1.8.1

NVD description

Envoy Gateway is an open source project for managing Envoy Proxy as a standalone or Kubernetes-based application gateway. Prior to 1.7.4 and 1.8.1, an HTTPRoute can use an extension-managed custom backendRef to reference a backend resource in another namespace without a matching Gateway API ReferenceGrant in the target namespace. The custom-backend branch in internal/gatewayapi/route.go omits validateBackendNamespace, allowing the route-owning namespace to bind to and use the resource without the backend namespace owner's consent and violating the Gateway API cross-namespace authorization model. This issue is fixed in versions 1.7.4 and 1.8.1.