Medium · published March 17, 2023
Cilium is a networking, observability, and security solution with an eBPF-based dataplane. Prior to versions 1.11.15, 1.12.8, and 1.13.1, an attacker with access to a Cilium agent pod can write to `/opt/cni/bin` due to a `hostPath` mount of that directory in the agent pod. By replacing the CNI binary with their own malicious binary and waiting for the creation of a new pod on the node, the attacker can gain access to the underlying node.
The issue has been fixed and the fix is available on versions 1.11.15, 1.12.8, and 1.13.1. Some workarounds are available. Kubernetes RBAC should be used to deny users and service accounts `exec` access to Cilium agent pods. In cases where a user requires `exec` access to Cilium agent pods, but should not have access to the underlying node, no workaround is possible.