Analyzing Docker Container Forensics

When to Use

• When investigating a compromised Docker container or container host
• For analyzing malicious Docker images pulled from registries
• During incident response involving containerized application breaches
• When examining container escape attempts or privilege escalation
• For auditing container configurations and identifying misconfigurations

Prerequisites

• Docker CLI access on the forensic workstation
• Access to the Docker host file system (forensic image or live)
• Understanding of Docker layered file system (overlay2, aufs)
• dive, docker-explorer, or container-diff for image analysis
• Knowledge of Docker daemon configuration and socket security
• Trivy or Grype for vulnerability scanning of container images

Workflow

Step 1: Preserve Container State and Evidence

bash
# List all containers (including stopped)
docker ps -a --no-trunc > /cases/case-2024-001/docker/container_list.txt

# Inspect the compromised container
CONTAINER_ID="abc123def456"
docker inspect $CONTAINER_ID > /cases/case-2024-001/docker/container_inspect.json

# Export container filesystem as tarball (preserves current state)
docker export $CONTAINER_ID > /cases/case-2024-001/docker/container_export.tar

# Create an image from the container's current state
docker commit $CONTAINER_ID forensic-evidence:case-2024-001
docker save forensic-evidence:case-2024-001 > /cases/case-2024-001/docker/container_image.tar

# Capture container logs
docker logs $CONTAINER_ID --timestamps > /cases/case-2024-001/docker/container_logs.txt 2>&1

# Capture running processes (if container is still running)
docker top $CONTAINER_ID > /cases/case-2024-001/docker/container_processes.txt

# Capture network connections
docker exec $CONTAINER_ID netstat -tlnp 2>/dev/null > /cases/case-2024-001/docker/container_network.txt

# Copy specific files from the container
docker cp $CONTAINER_ID:/var/log/ /cases/case-2024-001/docker/container_var_log/
docker cp $CONTAINER_ID:/tmp/ /cases/case-2024-001/docker/container_tmp/
docker cp $CONTAINER_ID:/etc/passwd /cases/case-2024-001/docker/container_passwd

# Hash all exported evidence
sha256sum /cases/case-2024-001/docker/*.tar > /cases/case-2024-001/docker/evidence_hashes.txt

Step 2: Analyze Container Image Layers

bash
# Install dive for image layer analysis
wget https://github.com/wagoodman/dive/releases/latest/download/dive_linux_amd64.deb
sudo dpkg -i dive_linux_amd64.deb

# Analyze image layers interactively
dive forensic-evidence:case-2024-001

# Non-interactive layer analysis
dive forensic-evidence:case-2024-001 --ci --json /cases/case-2024-001/docker/dive_analysis.json

# Extract and examine individual layers
mkdir -p /cases/case-2024-001/docker/layers/
tar -xf /cases/case-2024-001/docker/container_image.tar -C /cases/case-2024-001/docker/layers/

# List the image manifest and layer order
cat /cases/case-2024-001/docker/layers/manifest.json | python3 -m json.tool

# Examine each layer for changes
for layer in /cases/case-2024-001/docker/layers/*/layer.tar; do
    echo "=== Layer: $(dirname $layer | xargs basename) ==="
    tar -tf "$layer" | head -20
    echo "..."
done

# Use container-diff to compare with original base image
# Install container-diff
curl -LO https://storage.googleapis.com/container-diff/latest/container-diff-linux-amd64
chmod +x container-diff-linux-amd64

# Compare committed image with original
./container-diff-linux-amd64 diff daemon://nginx:latest daemon://forensic-evidence:case-2024-001 \
   --type=file --type=apt --type=history --json \
   > /cases/case-2024-001/docker/container_diff.json

Step 3: Examine Docker Host Artifacts

bash
# Docker data directory (default: /var/lib/docker/)
DOCKER_ROOT="/mnt/evidence/var/lib/docker"

# Examine overlay2 filesystem layers
ls -la $DOCKER_ROOT/overlay2/

# Find the container's merged filesystem
CONTAINER_HASH=$(docker inspect $CONTAINER_ID --format '{{.GraphDriver.Data.MergedDir}}' 2>/dev/null)
# Or manually from forensic image:
# Look in /var/lib/docker/containers/<container_id>/config.v2.json

# Analyze container configuration files
cat $DOCKER_ROOT/containers/$CONTAINER_ID/config.v2.json | python3 -m json.tool \
   > /cases/case-2024-001/docker/container_config.json

# Check Docker daemon configuration
cat /mnt/evidence/etc/docker/daemon.json 2>/dev/null > /cases/case-2024-001/docker/daemon_config.json

# Examine Docker events log
cat $DOCKER_ROOT/containers/$CONTAINER_ID/*.log > /cases/case-2024-001/docker/container_json_logs.txt

# Check for volume mounts (potential host filesystem access)
python3 << 'PYEOF'
import json

with open('/cases/case-2024-001/docker/container_inspect.json') as f:
    data = json.load(f)

inspect = data[0] if isinstance(data, list) else data

print("=== CONTAINER SECURITY ANALYSIS ===\n")

# Check mounts
print("Volume Mounts:")
for mount in inspect.get('Mounts', []):
    rw = "READ-WRITE" if mount.get('RW') else "READ-ONLY"
    print(f"  {mount.get('Source', 'N/A')} -> {mount.get('Destination', 'N/A')} ({rw})")
    if mount.get('Source') in ('/', '/etc', '/var', '/root') and mount.get('RW'):
        print(f"    WARNING: Sensitive host path mounted read-write!")

# Check privileged mode
host_config = inspect.get('HostConfig', {})
if host_config.get('Privileged'):
    print("\nWARNING: Container was running in PRIVILEGED mode!")

# Check capabilities
cap_add = host_config.get('CapAdd', [])
if cap_add:
    print(f"\nAdded Capabilities: {cap_add}")
    dangerous_caps = ['SYS_ADMIN', 'SYS_PTRACE', 'NET_ADMIN', 'SYS_MODULE']
    for cap in cap_add:
        if cap in dangerous_caps:
            print(f"  WARNING: Dangerous capability: {cap}")

# Check PID namespace
if host_config.get('PidMode') == 'host':
    print("\nWARNING: Container shares host PID namespace!")

# Check network mode
if host_config.get('NetworkMode') == 'host':
    print("\nWARNING: Container shares host network namespace!")

# Check user
user = inspect.get('Config', {}).get('User', 'root (default)')
print(f"\nRunning as user: {user}")

# Check environment variables for secrets
env_vars = inspect.get('Config', {}).get('Env', [])
print(f"\nEnvironment Variables: {len(env_vars)}")
for env in env_vars:
    key = env.split('=')[0]
    if any(s in key.upper() for s in ['PASSWORD', 'SECRET', 'KEY', 'TOKEN', 'CREDENTIAL']):
        print(f"  SENSITIVE: {key}=***REDACTED***")
PYEOF

Step 4: Analyze Container File System Changes

bash
# Compare container filesystem to original image
docker diff $CONTAINER_ID > /cases/case-2024-001/docker/filesystem_changes.txt

# A = Added, C = Changed, D = Deleted
# Analyze changes
python3 << 'PYEOF'
added = []
changed = []
deleted = []

with open('/cases/case-2024-001/docker/filesystem_changes.txt') as f:
    for line in f:
        line = line.strip()
        if line.startswith('A '):
            added.append(line[2:])
        elif line.startswith('C '):
            changed.append(line[2:])
        elif line.startswith('D '):
            deleted.append(line[2:])

print(f"Files Added: {len(added)}")
print(f"Files Changed: {len(changed)}")
print(f"Files Deleted: {len(deleted)}")

# Flag suspicious additions
suspicious = [f for f in added if any(s in f for s in
    ['/tmp/', '/dev/shm/', '/root/', '.sh', '.py', '.elf', 'reverse', 'shell', 'backdoor'])]
if suspicious:
    print(f"\nSuspicious Added Files:")
    for f in suspicious:
        print(f"  {f}")

# Flag suspicious changes
sus_changed = [f for f in changed if any(s in f for s in
    ['/etc/passwd', '/etc/shadow', '/etc/crontab', '/etc/ssh', '.bashrc'])]
if sus_changed:
    print(f"\nSuspicious Changed Files:")
    for f in sus_changed:
        print(f"  {f}")
PYEOF

# Extract and examine the container export
mkdir -p /cases/case-2024-001/docker/container_fs/
tar -xf /cases/case-2024-001/docker/container_export.tar -C /cases/case-2024-001/docker/container_fs/

# Scan for webshells and malicious files
find /cases/case-2024-001/docker/container_fs/tmp/ -type f -exec file {} \;
find /cases/case-2024-001/docker/container_fs/ -name "*.php" -newer /cases/case-2024-001/docker/container_fs/etc/hostname

Step 5: Scan for Vulnerabilities and Generate Report

bash
# Scan the image for known vulnerabilities
trivy image forensic-evidence:case-2024-001 \
   --format json \
   --output /cases/case-2024-001/docker/vulnerability_scan.json

# Scan the exported filesystem
trivy fs /cases/case-2024-001/docker/container_fs/ \
   --format table \
   --output /cases/case-2024-001/docker/fs_vulnerabilities.txt

# Check for secrets in the image
trivy image forensic-evidence:case-2024-001 \
   --scanners secret \
   --format json \
   --output /cases/case-2024-001/docker/secrets_scan.json

Key Concepts

| Concept | Description | |---------|-------------| | Image layers | Read-only filesystem layers stacked to form the container image | | overlay2 | Default Docker storage driver using union filesystem for layers | | Container diff | Comparison of runtime filesystem changes against the original image | | Privileged mode | Container with full host capabilities (bypasses most isolation) | | Docker socket | Unix socket (/var/run/docker.sock) controlling the Docker daemon | | Container escape | Technique for breaking out of container isolation to the host | | Volume mounts | Host filesystem paths made accessible inside the container | | Image history | Record of Dockerfile instructions used to build each layer |

Tools & Systems

| Tool | Purpose | |------|---------| | docker inspect | Detailed container configuration and state information | | docker diff | Show filesystem changes made in a running/stopped container | | dive | Interactive Docker image layer analysis tool | | container-diff | Google tool for comparing container image contents | | Trivy | Vulnerability scanner for container images and filesystems | | docker-explorer | Forensic tool for offline Docker artifact analysis | | Sysdig | Container runtime security monitoring and forensics | | Falco | Runtime threat detection for containers and Kubernetes |

Common Scenarios

Scenario 1: Web Application Container Compromise Export the container filesystem, identify webshells in web root, analyze access logs for exploitation attempts, check for added files and modified configurations, examine network connections for C2 communication, review container capabilities for escalation paths.

Scenario 2: Supply Chain Attack via Malicious Image Analyze image layers with dive to identify which layer added malicious content, compare with the official base image using container-diff, check image history for suspicious RUN commands, scan for embedded backdoors and cryptocurrency miners, trace the image pull from registry logs.

Scenario 3: Container Escape Investigation Check if container ran privileged or with dangerous capabilities, examine host filesystem mount points for unauthorized access, review Docker socket mount enabling Docker-in-Docker abuse, analyze host system logs for container escape indicators, check for kernel exploit artifacts.

Scenario 4: Cryptojacking in Container Environment Identify high-CPU containers, export and analyze the container image for mining binaries, check for unauthorized images in the registry, review container creation events for rogue deployments, examine network connections for mining pool communications.

Output Format

Docker Container Forensics Summary:
  Container: abc123def456 (nginx-app)
  Image: company/web-app:v2.1
  Status: Running (started 2024-01-10 09:00 UTC)
  Host: docker-host-01.corp.local

  Security Configuration:
    Privileged: No
    Capabilities Added: NET_ADMIN (WARNING)
    Volume Mounts: /var/log -> /host-logs (RW)
    Network Mode: bridge
    User: root (WARNING)

  Filesystem Changes:
    Added: 23 files (5 suspicious)
    Changed: 12 files (2 suspicious)
    Deleted: 0 files

  Suspicious Findings:
    /tmp/reverse.sh - Reverse shell script (Added)
    /var/www/html/.hidden/shell.php - PHP webshell (Added)
    /etc/crontab - Modified (persistence cron entry added)
    /root/.ssh/authorized_keys - Modified (unauthorized key added)

  Vulnerability Scan:
    Critical: 3 (CVE-2024-xxxx in base image)
    High: 12
    Medium: 34

  Evidence: /cases/case-2024-001/docker/