GHSA-qh36-44jv-c8xj Potential proxy IP restriction bypass in Kubernetes

• Go k8s.io/kubernetes: >= 1.21.0, <= 1.21.1 (no fix yet) • Go k8s.io/kubernetes: >= 1.20.0, <= 1.20.7 (no fix yet) • Go k8s.io/kubernetes: >= 1.19.0, <= 1.19.11 (no fix yet) • Go k8s.io/kubernetes: <= 1.18.19 (no fix yet)

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. All versions of Kubernetes are impacted, and there is no fix in place.