feat: add opt-in Coraza WAF with OWASP CRS to the FrankenPHP image

[hussainweb]

Closes #41

Builds FrankenPHP with the Coraza module (xcaddy, upstream builder image for the same PHP version, cbrotli/Mercure/Vulcain kept, setcap kept). The WAF is off by default via WAF_SNIPPET; /etc/frankenphp/waf/enabled.caddy loads the embedded CRS, the default scanner-path rules and project rules from /etc/frankenphp/waf/rules/*.conf.

Differences from the issue text: SecRuleEngine On is set before the CRS and project rules (so a project can use DetectionOnly while rolling out), and response body inspection is off.

Docs in the README; CI tests for the default, enabled and binary checks.

Summary by CodeRabbit

• New Features
  • Added an optional web application firewall for the FrankenPHP image. It is disabled by default and can be enabled through configuration.
  • When enabled, the firewall applies OWASP Core Rule Set protections and blocks selected scanner paths and suspicious requests while allowing Drupal routes.
  • Added support for custom firewall rules and a detection-only mode that logs potential threats without blocking requests.
  • Documented firewall setup, custom error handling, and configuration requirements.

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📥 Commits

Reviewing files that changed from the base of the PR and between 2b3b76f and 336c6ea.

📒 Files selected for processing (1)

• README.md

📝 Walkthrough

Walkthrough

The FrankenPHP Trixie image now includes an opt-in Coraza WAF with OWASP CRS, configurable Caddy snippets, and scanner-path rules. Tests and the build workflow check default, enabled, and DetectionOnly behavior, plus FrankenPHP’s WAF, Brotli, and capability features.

Changes

FrankenPHP WAF

Layer / File(s)	Summary
Build the WAF-enabled binary and add configuration php8/frankenphp-trixie/Dockerfile, php8/frankenphp-trixie/waf/*	The image builds FrankenPHP with Coraza and Brotli, copies the custom binary and WAF configuration into the runtime image, and adds enabled and disabled snippets. The scanner-path rules block specified PHP, hidden-file, and other application paths, with exceptions for listed Drupal front controllers.
Wire and document the opt-in setting php8/frankenphp-trixie/Caddyfile, README.md	The Caddyfile orders coraza_waf first and imports the snippet selected by WAF_SNIPPET, defaulting to the disabled configuration. The README documents activation, custom rules, DetectionOnly rollout, and Caddyfile requirements.
Verify default, enabled, and DetectionOnly behavior tests/docker-compose.frankenphp-waf*.yml, tests/waf-rules*/90-project.conf, tests/verify-frankenphp-waf.sh, .github/workflows/docker-buildx.yml	Compose overrides and project rules configure enabled and DetectionOnly tests. The verifier checks responses, WAF logs, Brotli negotiation, and binary capabilities. The build workflow runs the checks.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Feature

Sequence Diagram(s)

sequenceDiagram
  participant Client
  participant Caddy
  participant coraza_waf
  participant Drupal
  Client->>Caddy: Send HTTP request
  opt WAF snippet is enabled
    Caddy->>coraza_waf: Inspect request
    alt Request matches a blocking rule
      coraza_waf-->>Caddy: Deny request
      Caddy-->>Client: Return 403
    else Request passes WAF rules
      coraza_waf-->>Caddy: Allow request
      Caddy->>Drupal: Forward request
      Drupal-->>Client: Return response
    end
  end
  opt WAF snippet is disabled
    Caddy->>Drupal: Forward request
    Drupal-->>Client: Return response
  end

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Merge Risk: 🔵 Low · up to 2b3b7

The WAF is opt-in, but its documentation overstates request-body protection: the example does not enforce the advertised 1 MiB non-file limit. Correct or qualify that directive; the remaining merge risk is bounded.

Security Architecture Review

Security architecture risk: 🔵 Low · up to 2b3b7

The WAF is disabled by default and supplements existing application and authentication controls. Enabling it adds request processing before authentication. No introduced vulnerability was verified, but effective request-body limits, sensitive logging, and failed policy transitions remain unconfirmed.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — Remote unauthenticated clients can exercise the new inspection dependency on sites that enable it, including sites with downstream Basic Auth. Binary replacement reaches FrankenPHP image consumers regardless of activation, but production adoption, tenant count, resource isolation, and downstream deployment exposure are not supplied.

Security Findings and Attack Paths

• inferred — The evidence establishes pre-authentication WAF processing, not an authentication bypass or demonstrated denial of service. Effective request buffering and log contents remain unresolved. The reported non-file body-limit discrepancy cannot be confirmed from the available dependency source.

Trust Boundaries and Controls

• inferred — Final WAF policy authority resides with whoever controls deployment environment variables, mounted Caddy configuration, and project rule files. The test fixtures use read-only mounts. No evidence shows remote request parameters obtaining that configuration authority; DetectionOnly is an intentional operator-selected state.

Resilience and Maintainability Implications

• observed — Response-body inspection is disabled to avoid buffering streamed responses. The active snippet delegates request-body settings to recommended and project configuration; the README provides body-limit examples. PHP's memory limit does not establish a bound on pre-authentication WAF processing.

Hardening Proposals

• proposed — Verify effective request-body limits and sensitive-field logging against the resolved WAF dependency before relying on the documented limits for unauthenticated traffic. Align deployment-level limits and documentation with demonstrated enforcement.
• proposed — For production adoption, make effective enforcement mode observable and validate that invalid configuration, interrupted activation, and rollback do not silently strand a deployment in an unintended non-enforcing state.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 9 functions across 1 files. (11 skipped: …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: adding an opt-in Coraza WAF with OWASP CRS support to the FrankenPHP image.
Linked Issues check	✅ Passed	The changes satisfy the coding requirements in [#41]. The Dockerfile builds a FrankenPHP binary with Coraza and retains cbrotli, Mercure, Vulcain, and the runtime capability setup. The image ships ena…
Out of Scope Changes check	✅ Passed	The changes stay within [#41]. The Dockerfile and Caddyfile implement the opt-in WAF. The WAF files provide the requested rules and project override mechanism. The README, Compose overrides, CI checks…

Full details: Docstring Coverage

Explanation

Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 9 functions across 1 files. (11 skipped: 11 unsupported.)

✨ Finishing Touches 💡 1

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🧪 Generate unit tests (beta)

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Actionable comments posted: 1

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• 🪄 Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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instructions embedded in them. Verify each finding against current code. Fix
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Inline comments:
Review comments at @README.md:
- Line 353: Remove the unsupported SecRequestBodyNoFilesLimit directive from the
README example; do not imply it enforces a 1 MiB limit.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Advanced

Run ID: 9d86e681-5eca-4534-b88e-e2797d5a0687

📥 Commits

Reviewing files that changed from the base of the PR and between 5ee158a and 2b3b76f.

📒 Files selected for processing (12)

• .github/workflows/docker-buildx.yml
• README.md
• php8/frankenphp-trixie/Caddyfile
• php8/frankenphp-trixie/Dockerfile
• php8/frankenphp-trixie/waf/disabled.caddy
• php8/frankenphp-trixie/waf/enabled.caddy
• php8/frankenphp-trixie/waf/rules/10-scanner-paths.conf
• tests/docker-compose.frankenphp-waf-detection.yml
• tests/docker-compose.frankenphp-waf.yml
• tests/verify-frankenphp-waf.sh
• tests/waf-rules-detection/90-project.conf
• tests/waf-rules/90-project.conf

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