What’s Vulnerable › Vulnerabilities

CVE-2021-25736: Windows kube-proxy LoadBalancer contention

• Severity: medium (CVSS 6.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.9% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2023-10-30 · updated 2026-06-17
• Weakness: CWE-114

Description

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 products

• Kubernetes: from 1.18.0 before 1.18.18; from 1.19.0 before 1.19.10; from 1.20.0 before 1.20.6 — fixed in 1.18.18, 1.19.10, 1.20.6

How to fix

Upgrade to a fixed version: Kubernetes 1.18.18, 1.19.10, 1.20.6. Check the vendor advisory for mitigations.

References

• https://github.com/kubernetes/kubernetes/pull/99958
• https://groups.google.com/g/kubernetes-security-announce/c/lIoOPObO51Q/m/O15LOazPAgAJ
• https://security.netapp.com/advisory/ntap-20231221-0003/
• https://github.com/kubernetes/kubernetes/pull/99958
• https://groups.google.com/g/kubernetes-security-announce/c/lIoOPObO51Q/m/O15LOazPAgAJ
• https://security.netapp.com/advisory/ntap-20231221-0003/

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