CVE-2026-53718 is a medium-severity (CVSS 6.4) CWE-862 vulnerability in github.com/envoyproxy/gateway. A fix is available for github.com/envoyproxy/gateway — see the affected versions and patch details below.
Envoy Gateway custom backendRef cross-namespace ReferenceGrant bypass
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-53718.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
github.com/envoyproxy/gateway🐹github.com/envoyproxy/gatewayReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/envoyproxy/gateway | ≥ 1.8.0-rc.0&&< 1.8.1 | 1.8.1go get github.com/envoyproxy/gateway@v1.8.1 |
| 🐹Go | github.com/envoyproxy/gateway | all versions | 1.7.4go get github.com/envoyproxy/gateway@v1.7.4 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/envoyproxy/gateway, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/envoyproxy/gateway to 1.8.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-53718 is resolved across your whole dependency graph.
Workarounds
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Envoy Gateway as included in RHCL 1.3 and 1.4 is affected. A user permitted to create HTTPRoutes can use an extension-managed custom backend reference to access a resource in another namespace without the required ReferenceGrant.
No complete upstream workaround is available. Until a corrected build is installed, restrict untrusted users from creating HTTPRoutes with extension-managed custom backend references and audit cross-namespace references. The upstream fixes are 1.7.4 and 1.8.1.Source: Red Hat security advisory for CVE-2026-53718 (CC BY 4.0)
Frequently Asked Questions
Is CVE-2026-53718 in your dependencies?
Find it across Go, including transitive dependencies.