aeondave/container-technique

container-technique

Goal: Exploit container environments (Docker, Kubernetes, LXC) to achieve host-level code execution, horizontal pod movement, or cluster takeover.

When this technique applies

• You have gained a shell via Web RCE or SSH and notice .dockerenv, kubepods in cgroups, or specific mount patterns.
• You have acquired compromised Kubeconfigs or Service Account tokens.

The Escape Workflow

1. Internal Reconnaissance

Determine the isolation boundaries.

• Am I in a container?: ls -la /.dockerenv ; cat /proc/1/cgroup
• What privileges do I have?: capsh --print (look for CAP_SYS_ADMIN, CAP_SYS_MODULE, CAP_SYS_PTRACE).
• Network mapping: Look for kube-dns or metadata endpoints (e.g. 169.254.169.254 or GCP/Azure equivalents).

2. Hunting for Escape Vectors

• Exposed Docker Socket: ls -la /var/run/docker.sock. If writable, attach the host root filesystem to a new container.
• Privileged Container: If fdisk -l lists host drives or capsh shows CAP_SYS_ADMIN, mount the host filesystem (e.g., mount /dev/sda1 /mnt) or load a malicious kernel module.
• Cgroups Release Agent: If CAP_SYS_ADMIN is present, leverage the release_agent feature to spawn host processes.

3. Kubernetes Specifics

• Service Account Tokens: Located at /var/run/secrets/kubernetes.io/serviceaccount/.
• API Server Recon: Use curl -skH "Authorization: Bearer $TOKEN" https://$KUBERNETES_SERVICE_HOST/api/v1/namespaces/default/pods/
• Kubelet / ETCD Unauthenticated Ports: Check if ports 10250 (kubelet), 10255 (kubelet readonly), or 2379 (etcd) are exposed internally without authentication.

Quality Gates

• Do not break the pod: Kernel module injection and heavy cgroup manipulation can crash the container host. Perform checks first.
• Proof of Action: Once you escape, immediately collect evidence of reaching the underlying host (e.g., cat /etc/shadow from the host mount) rather than deploying destructive backdoors.

References

• references/privileged-escapes.md — Load when dealing with a container running with --privileged or CAP_SYS_ADMIN.