compose-lint 0.5.0

A security-focused linter for Docker Compose files

compose-lint

A security-focused linter for Docker Compose files. Catches dangerous misconfigurations before they reach production.

compose-lint targets the same niche Hadolint occupies for Dockerfiles: zero-config, opinionated, fast, and grounded in OWASP and CIS standards.

Installation

pip

pip install compose-lint

Docker — composelint/compose-lint

docker run --rm -v "$(pwd):/src" composelint/compose-lint

The image runs on Google's distroless Python (Debian 13, Python 3.13): no shell, no package manager, no apt, no pip at runtime. The entrypoint runs as nonroot (UID 65532). Only the Python interpreter, PyYAML, and compose_lint itself live in the final image — pip and the dist-info metadata are stripped from the venv after the build stage so Python-ecosystem CVEs don't surface on an unreachable binary. Multi-arch (linux/amd64 + linux/arm64), SHA-pinned base images bumped by Renovate, SLSA build provenance and Sigstore attestations published with every release. See ADR-009.

Quick Start

Run without arguments to auto-detect compose.yml, compose.yaml, docker-compose.yml, or docker-compose.yaml in the current directory:

compose-lint

Or pass files explicitly:

compose-lint docker-compose.yml docker-compose.prod.yml

Docker equivalent:

docker run --rm -v "$(pwd):/src" composelint/compose-lint docker-compose.prod.yml

Example Output

Given this docker-compose.yml:

services:
  traefik:
    image: traefik:v3.0@sha256:aaaabbbbccccddddeeeeffff00001111222233334444555566667777888899990
    read_only: true
    cap_drop: [ALL]
    security_opt:
      - no-new-privileges:true
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
    ports:
      - "8080:80"

and this .compose-lint.yml (suppressing CL-0001 for traefik with a tracked reason):

rules:
  CL-0001:
    exclude_services:
      traefik: "SEC-1234 approved — socket proxy planned for 2026-Q3"

running compose-lint docker-compose.yml produces:

compose-lint 0.3.7
files: docker-compose.yml  ·  config: .compose-lint.yml  ·  fail-on: high

docker-compose.yml:8  SUPPRESSED  CL-0001  Docker socket mounted via '/var/run/docker.sock:/var/run/docker.sock'. This gives the container full control over the Docker daemon.
  service: traefik
  reason: SEC-1234 approved — socket proxy planned for 2026-Q3

docker-compose.yml:10  HIGH      CL-0005  Port '8080:80' is bound to all interfaces. Docker bypasses host firewalls (UFW/firewalld), potentially exposing this port to the public internet.
  service: traefik
  fix: Bind to localhost: 127.0.0.1:8080:80
       If public access is needed, use a reverse proxy with TLS.
  ref: https://cheatsheetseries.owasp.org/cheatsheets/Docker_Security_Cheat_Sheet.html#rule-5a---be-careful-when-mapping-container-ports-to-the-host-with-firewalls-like-ufw
docker-compose.yml: 1 high  ·  1 suppressed (not counted)
✗ FAIL  ·  1 finding at or above high

Exit code is 1 (one finding at or above the default --fail-on high threshold). Suppressed findings are shown for auditability but do not count toward the threshold.

Rules

ID	Severity	Description	OWASP	CIS
CL-0001	CRITICAL	Docker socket mounted	Rule #1	5.31
CL-0002	CRITICAL	Privileged mode enabled	Rule #3	5.4
CL-0003	MEDIUM	Privilege escalation not blocked	Rule #4	5.25
CL-0004	MEDIUM	Image not pinned to version	Rule #13	5.27
CL-0005	HIGH	Ports bound to all interfaces	Rule #5a	5.13
CL-0006	MEDIUM	No capability restrictions	Rule #3	5.3
CL-0007	MEDIUM	Filesystem not read-only	Rule #8	5.12
CL-0008	HIGH	Host network mode	Rule #5	5.9
CL-0009	HIGH	Security profile disabled	Rule #6	5.21
CL-0010	HIGH	Host namespace sharing	Rule #3	5.8, 5.15, 5.16, 5.21
CL-0011	HIGH	Dangerous capabilities added	Rule #3	5.5
CL-0012	MEDIUM	PIDs cgroup limit disabled	—	5.29
CL-0013	HIGH	Sensitive host path mounted	Rule #8	5.5
CL-0014	MEDIUM	Logging driver disabled	—	5.x
CL-0015	LOW	Healthcheck disabled	—	4.6, 5.27
CL-0016	HIGH	Dangerous host device exposed	—	5.18
CL-0017	MEDIUM	Shared mount propagation	—	5.20
CL-0018	MEDIUM	Explicit root user	Rule #7	5.x
CL-0019	MEDIUM	Image tag without digest	Rule #13	5.27

Severity Levels

Findings are rated LOW, MEDIUM, HIGH, or CRITICAL based on exploitability and impact scope. See docs/severity.md for the full scoring matrix.

Configuration

Create .compose-lint.yml to disable rules or adjust severity:

rules:
  CL-0001:
    enabled: false
  CL-0003:
    enabled: false
    reason: "SEC-1234 — Approved by J. Smith, expires 2026-07-01"
  CL-0005:
    severity: medium

Disabled rules still run — findings appear as SUPPRESSED without affecting the exit code. The reason field is surfaced in all output formats:

• Text: shown after the SUPPRESSED label
• JSON: suppression_reason field
• SARIF: suppressions[].justification (recognized by GitHub Code Scanning)

To hide suppressed findings from output:

compose-lint --skip-suppressed docker-compose.yml

Per-service rule exclusions

When a rule is valid for some services but architecturally incompatible with others (e.g. CL-0003 no-new-privileges and an image whose entrypoint switches users), use exclude_services to suppress it for just the affected services while keeping it active elsewhere:

rules:
  CL-0003:
    exclude_services:
      minecraft: "entrypoint switches users via su-exec"
      backup: "forks as different user"
  CL-0007:
    exclude_services:
      - legacy-worker   # list form when no reason is needed

Excluded services still produce findings marked SUPPRESSED with the per-service reason flowing to suppression_reason / SARIF justification, same as a global disable. Service names are matched exactly; unknown names produce a stderr warning but do not error (Compose files are edited independently of config). Global enabled: false takes precedence over per-service exclusions.

CLI Reference

compose-lint [OPTIONS] [FILE ...]

  --format {text,json,sarif}  Output format (default: text)
  --fail-on SEVERITY          Minimum severity to trigger exit 1 (default: high)
  --skip-suppressed           Hide suppressed findings from output
  --config PATH               Path to config file (default: .compose-lint.yml)
  --explain CL-XXXX           Print the full documentation for a single rule
  --version                   Show version and exit

Exit Codes

Code	Meaning
0	No findings at or above the --fail-on threshold
1	One or more findings at or above the --fail-on threshold
2	Usage error (invalid args, file not found, invalid Compose file)

The default threshold is high — medium and low findings don't fail CI unless you opt in:

compose-lint --fail-on low docker-compose.yml   # fail on everything
compose-lint --fail-on critical docker-compose.yml  # only critical

CI Integration

GitHub Actions

The easiest path — runs compose-lint and uploads findings to GitHub Code Scanning:

# .github/workflows/lint.yml
name: Compose Lint
on: [push, pull_request]

jobs:
  compose-lint:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v6
      - uses: tmatens/compose-lint@v0.3.7
        with:
          sarif-file: results.sarif

Or install from PyPI directly:

      - uses: actions/setup-python@v6
        with:
          python-version: "3.13"
      - run: pip install compose-lint
      - run: compose-lint docker-compose.yml

SARIF output

compose-lint --format sarif docker-compose.yml > results.sarif

Pre-commit

# .pre-commit-config.yaml
repos:
  - repo: https://github.com/tmatens/compose-lint
    rev: v0.3.7
    hooks:
      - id: compose-lint

How it compares

Tool	Compose security rules	Scope	Zero config
compose-lint	Yes	Docker Compose	Yes
KICS	Yes	Broad IaC (Terraform, K8s, Compose, ...)	No
Hadolint	No — Dockerfile only	Dockerfile	Yes
dclint	Yes — schema/structure only	Docker Compose	Yes
Trivy	No — Dockerfile + image scanning	Dockerfiles, images, repos	Yes
Checkov	No — no Compose support	Broad IaC (Terraform, K8s, ...)	No

If you need broad IaC coverage across Terraform, Kubernetes, and more, KICS covers Docker Compose and is worth evaluating. If you want a lightweight, focused tool with zero config and actionable fix guidance for Compose files specifically, this is it.

Contributing

See CONTRIBUTING.md for development setup and how to add rules.

License

MIT