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CVE-2026-66794 – Unauthenticated SSRF / Auth Bypass – Red Hat Multicluster Engine for Kubernetes (cl

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Summary

CVE-2026-66794 is a critical unauthenticated Server-Side Request Forgery (SSRF) vulnerability affecting the cluster-proxy-addon component of Red Hat Multicluster Engine for Kubernetes. The flaw allows an attacker with network access to the component’s public-facing Route to bypass authentication and authorization controls entirely, and proxy arbitrary requests to internal services on any cluster managed by the hub. Red Hat rates the issue as Critical/Important with a CVSS v3.1 base score of 9.3.

Technical details

  • Root cause: The cluster-proxy-addon exposes a public Route terminated with TLS but without requiring client certificates or an OAuth proxy sidecar in front of it. The backend service handler performs no authentication or authorization checks on incoming requests.
  • Trigger conditions: The handler builds the outbound proxy target directly from user-controlled URL path segments, without validating them against an allowlist of permitted destinations.
  • Attack vector: An unauthenticated remote attacker who can reach the exposed Route over the network can craft requests that manipulate these path segments to redirect the proxy to arbitrary internal endpoints.
  • Impact: Successful exploitation lets the attacker use the multicluster hub as a pivot to reach services on any managed cluster that are not otherwise exposed externally, resulting in unauthorized access to internal services (high confidentiality impact, limited integrity impact, no direct availability impact per the CVSS vector).
  • The issue was identified via an internal AI-assisted static analysis audit (Red Hat-tracked finding CPA-2026-002) and reported to Red Hat on July 27, 2026.

Affected software

  • Red Hat Multicluster Engine for Kubernetes — component cluster-proxy-addon
  • Associated container images: multicluster-engine/cluster-proxy-addon-rhel9 and multicluster-engine/cluster-proxy-rhel9
  • Red Hat has not published a specific list of affected version ranges or fixed release versions in the current advisory/bug record; all currently deployed versions exposing the cluster-proxy-addon Route should be treated as potentially affected until a fix is confirmed.

Severity

  • CVSS v3.1 Base Score: 9.3 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:L/A:N
  • Red Hat internal severity rating: Important

Mitigation and recommended actions

  • Immediate: No fixed package version has been published by Red Hat at this time. Monitor the Red Hat CVE page and Bugzilla tracker (BZ#2507539) for an errata/RHSA release and apply the patched cluster-proxy-addon/cluster-proxy images as soon as they become available.
  • Workaround (until patched): Restrict network access to the cluster-proxy-addon user-facing Route to trusted networks only, using firewall rules or network policies to block inbound connections from untrusted or public sources. Do not expose this Route directly to the internet.
  • Review hub cluster logs for anomalous or unauthorized requests through the cluster-proxy-addon Route, particularly requests with manipulated or unexpected path segments targeting internal service endpoints.
  • Audit which managed-cluster services are reachable via the proxy and ensure sensitive internal services are otherwise network-isolated as defense in depth.

References

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