waf-setup

WAF Setup

Protect web applications with Web Application Firewalls.

Prerequisites

• Web application behind a load balancer or reverse proxy
• AWS account for AWS WAF, or Cloudflare account for Cloudflare WAF
• Nginx with ModSecurity module compiled for self-hosted WAF
• Access to application logs to tune rules and identify false positives
• Understanding of HTTP request/response structure

Before mutation, verify the owned account/zone/resource, existing rules and rollback plan. Save current configuration; creating duplicate phase entrypoints or applying Terraform can replace rules. Test the actual application in staging with representative allowed and disallowed requests, then promote a narrowly scoped blocking policy. The blocking examples below are desired enforcement states, not a recommendation to enable all rules immediately. Review sampled-request/log retention and redact tokens, cookies and bodies. WAFs do not replace application authorization, CSRF defenses, parameterized queries or dependency fixes.

AWS WAF

Create Web ACL with Managed Rules

# Create Web ACL with AWS managed rules
aws wafv2 create-web-acl \
  --name production-waf \
  --scope REGIONAL \
  --default-action Allow={} \
  --visibility-config SampledRequestsEnabled=true,CloudWatchMetricsEnabled=true,MetricName=production-waf \
  --rules file://waf-rules.json

Save the following reviewed JSON as waf-rules.json before creation. Inspect managed-rule versions and start with Count overrides and scoped test targets; tune and explicitly remove overrides only after evidence. AWS CLI byte-blob encoding depends on its binary-format setting: verify SearchString encoding for your CLI, rather than assuming the inline JSON is portable.

AWS WAF Rules Configuration

[
  {
    "Name": "AWSManagedRulesCommonRuleSet",
    "Priority": 1,
    "Statement": {
      "ManagedRuleGroupStatement": {
        "VendorName": "AWS",
        "Name": "AWSManagedRulesCommonRuleSet",
        "ExcludedRules": []
      }
    },
    "OverrideAction": { "None": {} },
    "VisibilityConfig": {
      "SampledRequestsEnabled": true,
      "CloudWatchMetricsEnabled": true,
      "MetricName": "AWSCommonRules"
    }
  },
  {
    "Name": "AWSManagedRulesSQLiRuleSet",
    "Priority": 2,
    "Statement": {
      "ManagedRuleGroupStatement": {
        "VendorName": "AWS",
        "Name": "AWSManagedRulesSQLiRuleSet"
      }
    },
    "OverrideAction": { "None": {} },
    "VisibilityConfig": {
      "SampledRequestsEnabled": true,
      "CloudWatchMetricsEnabled": true,
      "MetricName": "AWSSQLiRules"
    }
  },
  {
    "Name": "AWSManagedRulesKnownBadInputsRuleSet",
    "Priority": 3,
    "Statement": {
      "ManagedRuleGroupStatement": {
        "VendorName": "AWS",
        "Name": "AWSManagedRulesKnownBadInputsRuleSet"
      }
    },
    "OverrideAction": { "None": {} },
    "VisibilityConfig": {
      "SampledRequestsEnabled": true,
      "CloudWatchMetricsEnabled": true,
      "MetricName": "AWSBadInputRules"
    }
  },
  {
    "Name": "RateLimitRule",
    "Priority": 4,
    "Statement": {
      "RateBasedStatement": {
        "Limit": 2000,
        "AggregateKeyType": "IP"
      }
    },
    "Action": { "Block": {} },
    "VisibilityConfig": {
      "SampledRequestsEnabled": true,
      "CloudWatchMetricsEnabled": true,
      "MetricName": "RateLimit"
    }
  },
  {
    "Name": "GeoBlockRule",
    "Priority": 5,
    "Statement": {
      "GeoMatchStatement": {
        "CountryCodes": ["KP", "IR"]
      }
    },
    "Action": { "Block": {} },
    "VisibilityConfig": {
      "SampledRequestsEnabled": true,
      "CloudWatchMetricsEnabled": true,
      "MetricName": "GeoBlock"
    }
  },
  {
    "Name": "BlockBadUserAgents",
    "Priority": 6,
    "Statement": {
      "ByteMatchStatement": {
        "SearchString": "sqlmap",
        "FieldToMatch": { "SingleHeader": { "Name": "user-agent" } },
        "TextTransformations": [{ "Priority": 0, "Type": "LOWERCASE" }],
        "PositionalConstraint": "CONTAINS"
      }
    },
    "Action": { "Block": {} },
    "VisibilityConfig": {
      "SampledRequestsEnabled": true,
      "CloudWatchMetricsEnabled": true,
      "MetricName": "BadUserAgent"
    }
  }
]

Associate WAF with ALB

# Associate with Application Load Balancer
aws wafv2 associate-web-acl \
  --web-acl-arn arn:aws:wafv2:us-east-1:123456789012:regional/webacl/production-waf/abc123 \
  --resource-arn arn:aws:elasticloadbalancing:us-east-1:123456789012:loadbalancer/app/my-alb/abc123

# Associate with API Gateway
aws wafv2 associate-web-acl \
  --web-acl-arn arn:aws:wafv2:us-east-1:123456789012:regional/webacl/production-waf/abc123 \
  --resource-arn arn:aws:apigateway:us-east-1::/restapis/abc123/stages/prod

AWS WAF Terraform

resource "aws_wafv2_web_acl" "main" {
  name        = "production-waf"
  scope       = "REGIONAL"
  description = "Production WAF with OWASP protections"

  default_action {
    allow {}
  }

  rule {
    name     = "AWSManagedRulesCommonRuleSet"
    priority = 1

    override_action { none {} }

    statement {
      managed_rule_group_statement {
        name        = "AWSManagedRulesCommonRuleSet"
        vendor_name = "AWS"

        rule_action_override {
          name = "SizeRestrictions_BODY"
          action_to_use { count {} }
        }
      }
    }

    visibility_config {
      cloudwatch_metrics_enabled = true
      metric_name                = "AWSCommonRules"
      sampled_requests_enabled   = true
    }
  }

  rule {
    name     = "RateLimit"
    priority = 10

    action { block {} }

    statement {
      rate_based_statement {
        limit              = 2000
        aggregate_key_type = "IP"
      }
    }

    visibility_config {
      cloudwatch_metrics_enabled = true
      metric_name                = "RateLimit"
      sampled_requests_enabled   = true
    }
  }

  visibility_config {
    cloudwatch_metrics_enabled = true
    metric_name                = "production-waf"
    sampled_requests_enabled   = true
  }
}

resource "aws_wafv2_web_acl_association" "alb" {
  resource_arn = aws_lb.main.arn
  web_acl_arn  = aws_wafv2_web_acl.main.arn
}

Cloudflare WAF

API Configuration

Use an approved authenticated connector when available. For curl examples, CF_CURL_CONFIG refers to a user-provisioned private untracked config file (mode 0600) containing the authorization header; never pass the token in argv or print the file. Verify zone and token scope. Fetch the existing phase entrypoint/ruleset ID before any create/update, and merge intended changes without dropping other rules. The illustrative Cloudflare Terraform fragment uses provider v4-style blocks; pin and validate the actual provider schema before use.

# List available WAF rulesets
curl --fail-with-body --max-time 30 -sS "https://api.cloudflare.com/client/v4/zones/${ZONE_ID}/rulesets" \
  --config "$CF_CURL_CONFIG" | jq '.result[] | {id, name, phase}'

# Create a custom WAF rule
curl --fail-with-body --max-time 30 -X POST "https://api.cloudflare.com/client/v4/zones/${ZONE_ID}/rulesets" \
  --config "$CF_CURL_CONFIG" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "Custom WAF Rules",
    "kind": "zone",
    "phase": "http_request_firewall_custom",
    "rules": [
      {
        "action": "block",
        "expression": "(http.request.uri.query contains \"union select\" or http.request.uri.query contains \"1=1\")",
        "description": "Block SQL injection patterns in query string"
      },
      {
        "action": "block",
        "expression": "(http.request.uri.path contains \"..%2f\" or http.request.uri.path contains \"..%5c\")",
        "description": "Block path traversal attempts"
      },
      {
        "action": "managed_challenge",
        "expression": "(http.request.uri.path eq \"/login\")",
        "description": "Illustrative login challenge; enable only after application testing"
      },
      {
        "action": "block",
        "expression": "(lower(http.user_agent) contains \"sqlmap\" or lower(http.user_agent) contains \"nikto\")",
        "description": "Block known attack tools"
      }
    ]
  }'

# Configure rate limiting
curl --fail-with-body --max-time 30 -X POST "https://api.cloudflare.com/client/v4/zones/${ZONE_ID}/rulesets" \
  --config "$CF_CURL_CONFIG" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "Rate Limiting",
    "kind": "zone",
    "phase": "http_ratelimit",
    "rules": [
      {
        "action": "block",
        "ratelimit": {
          "characteristics": ["cf.colo.id", "ip.src"],
          "period": 60,
          "requests_per_period": 100,
          "mitigation_timeout": 600
        },
        "expression": "(starts_with(http.request.uri.path, \"/api/\"))",
        "description": "Rate limit API endpoints"
      }
    ]
  }'

Cloudflare Terraform

resource "cloudflare_ruleset" "waf_custom" {
  zone_id = var.zone_id
  name    = "Custom WAF Rules"
  kind    = "zone"
  phase   = "http_request_firewall_custom"

  rules {
    action      = "block"
    expression  = "(http.request.uri.query contains \"union select\")"
    description = "Block SQL injection in query string"
  }

  rules {
    action      = "managed_challenge"
    expression  = "(http.request.uri.path eq \"/login\")"
    description = "Illustrative login challenge; do not use on non-browser API clients"
  }
}

Cloudflare cf.threat_score now always returns zero; do not use old score thresholds as protection. The login challenge above is an explicit path example, not a replacement threat score. Query substring and User-Agent rules are evadable and can block legitimate requests; use managed rules and application fixes. Rate-limit options and periods depend on the plan; confirm them before sending. Geo blocks require business authorization and are not proof of attacker origin.

Contents

• ModSecurity with Nginx
• WAF Tuning Workflow
• Troubleshooting
• Best Practices
• Related Skills

When to Use This Skill

Use this skill when:

• Deploying a public-facing web application that needs attack protection
• Meeting compliance requirements (PCI-DSS, SOC2) for web application security
• Blocking OWASP Top 10 attack categories (SQLi, XSS, CSRF, etc.)
• Protecting APIs from abuse, injection, and rate-based attacks
• Adding a virtual patching layer while application code is being fixed

Limitations

• Apply guidance only within authorized scope; test destructive steps in non-production first.
• Docs-only import: upstream scripts and templates not bundled.

Example

# Read-only first: inventory before any active step.
which <tool> && <tool> --help | head -n 20

Adapted from BagelHole/DevOps-Security-Agent-Skills (MIT); frontmatter, When to Use/Limitations, and safety boundaries added for upstream compliance. Docs-only import: helper scripts and templates not bundled.