CVE-2021-25736 Windows kube-proxy LoadBalancer contention

What is CVE-2021-25736?

CVE-2021-25736 is a medium-severity server-side request forgery vulnerability in Kubernetes Kubernetes, published on 30 Oct 2023. An attacker needs administrator access to exploit it, with no action from the victim.

Official 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.

Weakness: CWE-114

Which versions are affected by CVE-2021-25736?

3 open source packages ship an affected version, including k8s.io/kubernetes. It affects 1 product.

Products include Kubernetes Kubernetes.

How do I fix CVE-2021-25736?

Upgrade k8s.io/kubernetes to 1.21.0 or later.

Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.

Is CVE-2021-25736 being exploited?

There is no known exploitation of CVE-2021-25736 in the wild and no public exploit code.

Other vulnerabilities in Kubernetes Kubernetes

• CVE-2018-1002105 Privilege Escalation in Kubernetes Critical 9.8
• CVE-2017-1000056 Kubernetes Privilege Escalation Critical 9.8
• CVE-2016-1906 Authorization bypass in Openshift Critical 9.8
• CVE-2023-3676 Kubernetes - Windows nodes - Insufficient input sanitization leads to privilege escalation High 8.8
• CVE-2023-3955 Kubernetes - Windows nodes - Insufficient input sanitization leads to privilege escalation High 8.8

All Kubernetes Kubernetes vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-35c7-w35f-xwgh, GO-2023-2159.