CVE-2021-25737 Holes in EndpointSlice Validation Enable Host Network Hijack

What is CVE-2021-25737?

CVE-2021-25737 is a low-severity server-side request forgery vulnerability in Kubernetes Kubernetes, published on 6 Sep 2021. An attacker needs administrator access to exploit it, with no action from the victim.

Official description

A security issue was discovered in Kubernetes where a user may be able to redirect pod traffic to private networks on a Node. Kubernetes already prevents creation of Endpoint IPs in the localhost or link-local range, but the same validation was not performed on EndpointSlice IPs.

Weakness: CWE-601, CWE-184

Which versions are affected by CVE-2021-25737?

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

Products include Kubernetes Kubernetes.

How do I fix CVE-2021-25737?

Upgrade k8s.io/kubernetes to a fixed version for your release line: 1.18.19, 1.19.11, 1.20.7 or 1.21.1.

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

Is CVE-2021-25737 being exploited?

There is no known exploitation of CVE-2021-25737 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 CLEANSTART-2025-VV56547, CLEANSTART-2026-TF89729, DEBIAN-CVE-2021-25737, GHSA-mfv7-gq43-w965, GO-2022-0908.