Hardening Docker Daemon Configuration

What it does

When your agent uses it

• Securing a Docker hosts daemon to prevent privilege escalation
• Lateral movement
• Auditing daemon settings against CIS requirements
• Hardening images and per-container runtime flags - use hardening-docker-containers-for-production

Example prompts

• “Use the hardening-docker-daemon-configuration skill to harden the Docker daemon (dockerd) through /etc/docker/daemon.json with user namespace…”
• “/hardening-docker-daemon-configuration”

Requirements

• Python 3
• Docker

Workflow steps

10 steps, taken from the first numbered list in SKILL.md.

1. 1Never expose Docker daemon without TLS - Always use --tlsverify for remote access
2. 2Enable user namespace remapping - Map container root to unprivileged host UID
3. 3Disable ICC - Prevent default bridge network container-to-container communication
4. 4Use rootless mode - Run Docker daemon as non-root where possible
5. 5Enable content trust - Only pull signed images
6. 6Configure log rotation - Prevent log files from filling disk
7. 7Use seccomp profiles - Restrict syscalls available to containers
8. 8Audit Docker socket - Monitor access to /var/run/docker.sock
9. 9Run Docker Bench regularly - Automate CIS benchmark checks
10. 10Keep Docker updated - Apply security patches promptly

What it can do on your machine

Read from SKILL.md and the folder at commit 54a7988. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  Ships 2 files in scripts/ (Python), which the agent can run.

  Shell commands in SKILL.md call:

  • docker
  • openssl
  • curl
  • sh

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  Hosts in commands or code, which the agent is likely to contact:

  • get.docker.com

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names no API keys, tokens, secrets or passwords.

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Hardening Docker Daemon Configuration loads about 2.1k tokens when it runs, and up to ~3.9k if it reads all its reference files. Until then it costs about 160 tokens; SKILL.md has 346 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~160

When it runs · the whole SKILL.md, loaded when a task matches

~2.1k

With references · SKILL.md plus every file in references/, read only if the agent opens them

~3.9k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

• NoteRuns commands with sudoSKILL.md:53

  - Root or sudo access to the Docker host

• NoteRuns commands with sudoSKILL.md:207

  sudo mkdir -p /etc/docker/tls

• NoteRuns commands with sudoSKILL.md:208

  sudo cp ca.pem server-cert.pem server-key.pem /etc/docker/tls/

• NoteRuns commands with sudoSKILL.md:238

  sudo chown root:docker /var/run/docker.sock

• NoteRuns commands with sudoSKILL.md:239

  sudo chmod 660 /var/run/docker.sock

• NoteRuns commands with sudoSKILL.md:242

  sudo auditctl -w /var/run/docker.sock -k docker-socket

• NotePipes a well-known installer script into a shellSKILL.md:252

  curl -fsSL https://get.docker.com/rootless | sh

• NoteRuns commands with sudoSKILL.md:298

  sudo aa-status

• NoteRuns commands with sudoSKILL.md:304

  sudo apparmor_parser -r /etc/apparmor.d/docker-custom

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); the scripts in this folder are not scanned.

SKILL.md

The full file from mukul975/Anthropic-Cybersecurity-Skills at commit 54a7988, republished under its Apache-2.0 licence (© mukul975). 346 words, ~2,146 tokens.

name

hardening-docker-daemon-configuration

description

Hardens the Docker daemon (dockerd) through /etc/docker/daemon.json with user namespace remapping, TLS client authentication, seccomp profiles, and CIS Docker Benchmark controls such as icc, no-new-privileges, and live-restore. Use when securing a Docker host's daemon to prevent privilege escalation, breakout, or lateral movement, or when auditing daemon settings against CIS requirements. Keywords: dockerd, daemon.json, userns-remap, no-new-privileges, icc, live-restore, TLS socket. Do not use for hardening images and per-container runtime flags - use hardening-docker-containers-for-production.

domain

cybersecurity

subdomain

container-security

tags

docker, daemon-hardening, container-security, cis-benchmark, rootless, userns-remap

version

1.0

author

mahipal

license

Apache-2.0

nist_csf

PR.PS-01, PR.IR-01, ID.AM-08, DE.CM-01

mitre_attack

T1610, T1611, T1609, T1525, T1553

{
  "icc": false,
  "userns-remap": "default",
  "no-new-privileges": true,
  "log-driver": "json-file",
  "log-opts": {
    "max-size": "10m",
    "max-file": "5"
  },
  "storage-driver": "overlay2",
  "live-restore": true,
  "userland-proxy": false,
  "default-ulimits": {
    "nofile": {
      "Name": "nofile",
      "Hard": 65536,
      "Soft": 32768
    },
    "nproc": {
      "Name": "nproc",
      "Hard": 4096,
      "Soft": 2048
    }
  },
  "seccomp-profile": "/etc/docker/seccomp/default.json",
  "default-address-pools": [
    {
      "base": "172.17.0.0/16",
      "size": 24
    }
  ],
  "iptables": true,
  "ip-forward": true,
  "ip-masq": true,
  "experimental": false,
  "metrics-addr": "127.0.0.1:9323",
  "max-concurrent-downloads": 3,
  "max-concurrent-uploads": 5,
  "default-runtime": "runc",
  "runtimes": {
    "runsc": {
      "path": "/usr/local/bin/runsc",
      "runtimeArgs": ["--platform=ptrace"]
    }
  }
}

{
  "icc": false
}

{
  "userns-remap": "default"
}

# Verify userns-remap is active
cat /etc/subuid
# Output: dockremap:100000:65536

cat /etc/subgid
# Output: dockremap:100000:65536

# Verify container UID mapping
docker run --rm alpine id
# uid=0(root) gid=0(root) -- but host UID is 100000+

{
  "no-new-privileges": true
}

{
  "live-restore": true
}

{
  "userland-proxy": false
}

# Create CA
openssl genrsa -aes256 -out ca-key.pem 4096
openssl req -new -x509 -days 365 -key ca-key.pem -sha256 -out ca.pem \
  -subj "/CN=Docker CA"

# Create server key and CSR
openssl genrsa -out server-key.pem 4096
openssl req -subj "/CN=docker-host" -sha256 -new -key server-key.pem -out server.csr

# Create extfile with SANs
echo "subjectAltName = DNS:docker-host,IP:10.0.0.5,IP:127.0.0.1" > extfile.cnf
echo "extendedKeyUsage = serverAuth" >> extfile.cnf

# Sign server certificate
openssl x509 -req -days 365 -sha256 -in server.csr -CA ca.pem -CAkey ca-key.pem \
  -CAcreateserial -out server-cert.pem -extfile extfile.cnf

# Create client key and certificate
openssl genrsa -out key.pem 4096
openssl req -subj "/CN=client" -new -key key.pem -out client.csr
echo "extendedKeyUsage = clientAuth" > extfile-client.cnf
openssl x509 -req -days 365 -sha256 -in client.csr -CA ca.pem -CAkey ca-key.pem \
  -CAcreateserial -out cert.pem -extfile extfile-client.cnf

# Set permissions
chmod 0400 ca-key.pem key.pem server-key.pem
chmod 0444 ca.pem server-cert.pem cert.pem

# Move to Docker TLS directory
sudo mkdir -p /etc/docker/tls
sudo cp ca.pem server-cert.pem server-key.pem /etc/docker/tls/

{
  "tls": true,
  "tlsverify": true,
  "tlscacert": "/etc/docker/tls/ca.pem",
  "tlscert": "/etc/docker/tls/server-cert.pem",
  "tlskey": "/etc/docker/tls/server-key.pem",
  "hosts": ["unix:///var/run/docker.sock", "tcp://0.0.0.0:2376"]
}

docker --tlsverify \
  --tlscacert=ca.pem \
  --tlscert=cert.pem \
  --tlskey=key.pem \
  -H=tcp://docker-host:2376 version

# Restrict socket ownership
sudo chown root:docker /var/run/docker.sock
sudo chmod 660 /var/run/docker.sock

# Audit Docker socket access
sudo auditctl -w /var/run/docker.sock -k docker-socket

# Never mount Docker socket into containers
# BAD: docker run -v /var/run/docker.sock:/var/run/docker.sock ...

# Install rootless Docker
curl -fsSL https://get.docker.com/rootless | sh

# Configure environment
export PATH=$HOME/bin:$PATH
export DOCKER_HOST=unix://$XDG_RUNTIME_DIR/docker.sock

# Start rootless daemon
systemctl --user start docker
systemctl --user enable docker

# Verify rootless mode
docker info | grep -i rootless
# Rootless: true

# Enable Docker Content Trust
export DOCKER_CONTENT_TRUST=1

# Pull only signed images
docker pull library/alpine:3.18
# Will fail if image is not signed

# Sign and push image
docker trust sign myregistry/myapp:1.0

# View default seccomp profile
docker info --format '{{.SecurityOptions}}'

# Use custom seccomp profile
docker run --security-opt seccomp=/etc/docker/seccomp/custom.json alpine

# Verify seccomp is enabled
docker inspect --format='{{.HostConfig.SecurityOpt}}' container_name

# Check AppArmor status
sudo aa-status

# Use custom AppArmor profile
docker run --security-opt apparmor=docker-custom alpine

# Load custom profile
sudo apparmor_parser -r /etc/apparmor.d/docker-custom

# Check daemon configuration
docker info

# Verify userns-remap
docker info --format '{{.SecurityOptions}}'

# Check ICC setting
docker network inspect bridge --format '{{.Options}}'

# Audit with Docker Bench
docker run --rm --net host --pid host \
  -v /var/run/docker.sock:/var/run/docker.sock \
  -v /etc:/etc:ro \
  docker/docker-bench-security

© mukul975, Apache-2.0. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 7 other files (scripts, references, assets) in skills/hardening-docker-daemon-configuration of mukul975/Anthropic-Cybersecurity-Skills.

• SKILL.md
• LICENSE
• assets/template.md
• references/api-reference.md
• references/standards.md
• references/workflows.md
• scripts/agent.py
• scripts/process.py

Open the folder on GitHubat commit 54a7988