BIT-envoy-gateway-2026-53718: Envoy Gateway custom backendRef cross-namespace ReferenceGrant bypass

Q: Who is exposed to this issue?

Deployments of Envoy Gateway before 1.7.4 or 1.8.1 are affected when HTTPRoutes use extension-managed custom backendRefs that point to resources in a different namespace.

Q: What does an attacker need to exploit it?

An attacker needs permission to create or modify an HTTPRoute in a route-owning namespace and must be able to configure an extension-managed custom backendRef targeting a resource in another namespace.

Q: Are cross-namespace custom backend references protected by a ReferenceGrant?

Not in the affected versions. The custom-backend handling omits backend namespace validation, so it can bind to a cross-namespace backend resource without a matching ReferenceGrant from the target namespace owner.

Q: What should be done if patching cannot happen immediately?

Restrict who can create or modify HTTPRoutes, and review or prevent extension-managed custom backendRefs that target resources outside the route's namespace. Upgrade to 1.7.4 or 1.8.1 when possible.

Q: How can teams identify potentially affected routes?

Review HTTPRoutes for extension-managed custom backendRefs whose referenced backend resource is in a namespace different from the HTTPRoute. Routes with such references are suspicious if the target namespace does not have a matching Gateway API ReferenceGrant.

Published Sep 14, 2026

Updated

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.

Affected Software

1 affected component

Envoy Envoy Gateway<1.7.4, =1.8.0

Remediation

Recommended actions to resolve this vulnerability, in priority order.

Upgrade
Upgrade Envoy Gateway to a version that resolves this vulnerability.
Fixed in 1.7.4
Upgrade
Upgrade Envoy Gateway to a version that resolves this vulnerability.
Fixed in 1.8.1

Event History

Sep 14, 2026

CVE Published

via OSV·08:12 PM

Data Sourced

via OSV·08:12 PM

DescriptionSeverityWeakness

Frequently Asked Questions

Who is exposed to this issue?

Deployments of Envoy Gateway before 1.7.4 or 1.8.1 are affected when HTTPRoutes use extension-managed custom backendRefs that point to resources in a different namespace.

What does an attacker need to exploit it?

An attacker needs permission to create or modify an HTTPRoute in a route-owning namespace and must be able to configure an extension-managed custom backendRef targeting a resource in another namespace.

Are cross-namespace custom backend references protected by a ReferenceGrant?

Not in the affected versions. The custom-backend handling omits backend namespace validation, so it can bind to a cross-namespace backend resource without a matching ReferenceGrant from the target namespace owner.

What should be done if patching cannot happen immediately?

Restrict who can create or modify HTTPRoutes, and review or prevent extension-managed custom backendRefs that target resources outside the route's namespace. Upgrade to 1.7.4 or 1.8.1 when possible.

How can teams identify potentially affected routes?

Review HTTPRoutes for extension-managed custom backendRefs whose referenced backend resource is in a namespace different from the HTTPRoute. Routes with such references are suspicious if the target namespace does not have a matching Gateway API ReferenceGrant.

BIT-envoy-gateway-2026-53718: Envoy Gateway custom backendRef cross-namespace ReferenceGrant bypass

Affected Software

Remediation

Event History

Frequently Asked Questions

Who is exposed to this issue?

What does an attacker need to exploit it?

Are cross-namespace custom backend references protected by a ReferenceGrant?

What should be done if patching cannot happen immediately?

How can teams identify potentially affected routes?

Company

Resources

Contact

Frequently Asked Questions

Who is exposed to this issue?

What does an attacker need to exploit it?

Are cross-namespace custom backend references protected by a ReferenceGrant?

What should be done if patching cannot happen immediately?

How can teams identify potentially affected routes?