Bypass of Kubernetes API Server proxy TOCTOU

Vulnerability Description

As mitigations to a report from 2019 and CVE-2020-8555, Kubernetes attempts to prevent proxied connections from accessing link-local or localhost networks when making user-driven connections to Services, Pods, Nodes, or StorageClass service providers. As part of this mitigation Kubernetes does a DNS name resolution check and validates that response IPs are not in the link-local (169.254.0.0/16) or localhost (127.0.0.0/8) range. Kubernetes then performs a second DNS resolution without validation for the actual connection. If a non-standard DNS server returns different non-cached responses, a user may be able to bypass the proxy IP restriction and access private networks on the control plane.

References

• https://kubernetes.io/blog/2026/05/26/reconciling-unfixed-kubernetes-cves/
• https://github.com/kubernetes/kubernetes/issues/101493
• https://groups.google.com/g/kubernetes-security-announce/c/-MFX60_wdOY
• https://security.netapp.com/advisory/ntap-20220225-0002/