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Date: Tue, 11 May 2021 03:39:45 +0000
From: Swamy Shivaganga Nagaraju <>
To: "" <>
Subject: [Kubernetes] CVE-2021-25736: Windows kube-proxy LoadBalancer


A security issue was discovered in the Windows version of kube-proxy where a process on a Node may be able to accept traffic intended for a LoadBalancer Service. Clusters without Windows nodes are unaffected.

This issue has been rated Medium (CVSS:3.0/AV:N/AC:H/PR:H/UI:N/S:C/C:H/I:N/A:N<>)), and assigned CVE-2021-25736.

Kube-proxy on Windows can unintentionally forward traffic to local processes listening on the same port ("spec.ports[*].port") as a LoadBalancer Service when the LoadBalancer controller does not set the "status.loadBalancer.ingress[].ip" field. Clusters where the LoadBalancer controller sets the "status.loadBalancer.ingress[].ip" field are unaffected.

Affected Components and Configurations

Windows kube-proxy. Clusters with Windows nodes are affected by this vulnerability.

Affected Versions

  *   Kubernetes <= v1.20.5
  *   Kubernetes <= v1.19.9
  *   Kubernetes <= v1.18.17

Fixed Versions

This issue has been fixed in the following versions:

  *   v1.21.0
  *   v1.20.6
  *   v1.19.10
  *   v1.18.18




Unexpected processes listening on the same port as used by a LoadBalancer service could indicate exploitation of this issue, and should be investigated.

If you find evidence that this vulnerability has been exploited, please contact<>

Additional Details
See the GitHub issue for more details:


This vulnerability was discovered by  Eric Paris & Christian Hernandez from Red Hat.

Thank You,

  Swamy Shivaganga Nagaraju, on behalf of the Kubernetes Product Security Committee

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