Implementing Cloud WAF Rules

When to Use

When deploying new web applications or APIs behind cloud load balancers requiring OWASP protection
When application penetration testing reveals SQL injection, XSS, or other injection vulnerabilities
When experiencing brute force, credential stuffing, or bot attacks against authentication endpoints
When compliance requirements mandate a WAF for PCI-DSS or similar standards
When tuning WAF rules to reduce false positives blocking legitimate application traffic

Do not use for network-level DDoS protection (use AWS Shield or Azure DDoS Protection), for API authentication design (see managing-cloud-identity-with-okta), or for application code-level security fixes (WAF is a compensating control, not a replacement for secure code).

Prerequisites

AWS ALB/CloudFront, Azure Application Gateway, or Cloudflare configured as the application entry point
Application traffic logs for baseline analysis before WAF deployment
Test environment for validating WAF rules before production enforcement
Understanding of application request patterns to minimize false positives

Workflow

Step 1: Deploy Managed Rule Sets

Enable cloud provider managed rule sets that cover OWASP Top 10 vulnerabilities. Start in Count (detection) mode before switching to Block (prevention) mode.

# AWS WAF: 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 '[
    {
      "Name": "AWSManagedRulesCommonRuleSet",
      "Priority": 1,
      "Statement": {
        "ManagedRuleGroupStatement": {
          "VendorName": "AWS",
          "Name": "AWSManagedRulesCommonRuleSet"
        }
      },
      "OverrideAction": {"Count": {}},
      "VisibilityConfig": {
        "SampledRequestsEnabled": true,
        "CloudWatchMetricsEnabled": true,
        "MetricName": "CommonRuleSet"
      }
    },
    {
      "Name": "AWSManagedRulesSQLiRuleSet",
      "Priority": 2,
      "Statement": {
        "ManagedRuleGroupStatement": {
          "VendorName": "AWS",
          "Name": "AWSManagedRulesSQLiRuleSet"
        }
      },
      "OverrideAction": {"Count": {}},
      "VisibilityConfig": {
        "SampledRequestsEnabled": true,
        "CloudWatchMetricsEnabled": true,
        "MetricName": "SQLiRuleSet"
      }
    },
    {
      "Name": "AWSManagedRulesKnownBadInputsRuleSet",
      "Priority": 3,
      "Statement": {
        "ManagedRuleGroupStatement": {
          "VendorName": "AWS",
          "Name": "AWSManagedRulesKnownBadInputsRuleSet"
        }
      },
      "OverrideAction": {"Count": {}},
      "VisibilityConfig": {
        "SampledRequestsEnabled": true,
        "CloudWatchMetricsEnabled": true,
        "MetricName": "KnownBadInputs"
      }
    }
  ]'

Step 2: Create Custom Rate Limiting Rules

Deploy rate-based rules to protect login endpoints against brute force and credential stuffing attacks.

# Rate limiting rule for login endpoint (100 requests per 5 minutes per IP)
aws wafv2 update-web-acl \
  --name production-waf \
  --scope REGIONAL \
  --id <web-acl-id> \
  --lock-token <lock-token> \
  --default-action '{"Allow": {}}' \
  --rules '[
    {
      "Name": "RateLimitLogin",
      "Priority": 0,
      "Statement": {
        "RateBasedStatement": {
          "Limit": 100,
          "AggregateKeyType": "IP",
          "ScopeDownStatement": {
            "ByteMatchStatement": {
              "FieldToMatch": {"UriPath": {}},
              "PositionalConstraint": "STARTS_WITH",
              "SearchString": "/api/auth/login",
              "TextTransformations": [{"Priority": 0, "Type": "LOWERCASE"}]
            }
          }
        }
      },
      "Action": {"Block": {"CustomResponse": {"ResponseCode": 429}}},
      "VisibilityConfig": {
        "SampledRequestsEnabled": true,
        "CloudWatchMetricsEnabled": true,
        "MetricName": "RateLimitLogin"
      }
    }
  ]'

Step 3: Configure Geo-Blocking and IP Reputation

Block traffic from countries where the application has no legitimate users and leverage IP reputation lists to block known malicious sources.

# AWS WAF: Geo-blocking rule
# Block countries not in the allowed list
aws wafv2 create-ip-set \
  --name blocked-ips \
  --scope REGIONAL \
  --ip-address-version IPV4 \
  --addresses "198.51.100.0/24" "203.0.113.0/24"

# Add Amazon IP Reputation rule
# AWSManagedRulesAmazonIpReputationList blocks IPs flagged by AWS threat intelligence

Step 4: Tune Rules to Reduce False Positives

Analyze WAF logs in Count mode to identify legitimate requests being flagged. Create rule exceptions for specific URI paths or request patterns.

# Enable WAF logging to S3
aws wafv2 put-logging-configuration \
  --logging-configuration '{
    "ResourceArn": "arn:aws:wafv2:us-east-1:123456789012:regional/webacl/production-waf/id",
    "LogDestinationConfigs": ["arn:aws:s3:::waf-logs-bucket"],
    "RedactedFields": [{"SingleHeader": {"Name": "authorization"}}]
  }'

# Query WAF logs with Athena to find false positives
# Find rules triggered most frequently for legitimate traffic
cat << 'EOF' > waf-analysis.sql
SELECT
  terminatingRuleId,
  httpRequest.uri,
  httpRequest.httpMethod,
  COUNT(*) as block_count
FROM waf_logs
WHERE action = 'BLOCK'
  AND timestamp > date_add('day', -7, now())
GROUP BY terminatingRuleId, httpRequest.uri, httpRequest.httpMethod
ORDER BY block_count DESC
LIMIT 20
EOF

# Exclude specific rule from managed rule set that causes false positives
# Example: Exclude SizeRestrictions_BODY for file upload endpoint
aws wafv2 update-web-acl \
  --name production-waf \
  --scope REGIONAL \
  --id <web-acl-id> \
  --lock-token <lock-token> \
  --rules '[{
    "Name": "AWSManagedRulesCommonRuleSet",
    "Priority": 1,
    "Statement": {
      "ManagedRuleGroupStatement": {
        "VendorName": "AWS",
        "Name": "AWSManagedRulesCommonRuleSet",
        "ExcludedRules": [{"Name": "SizeRestrictions_BODY"}]
      }
    },
    "OverrideAction": {"None": {}},
    "VisibilityConfig": {
      "SampledRequestsEnabled": true,
      "CloudWatchMetricsEnabled": true,
      "MetricName": "CommonRuleSet"
    }
  }]'

Step 5: Switch to Block Mode After Validation

After 7-14 days of Count mode with acceptable false positive rates, switch managed rules to Block mode for active protection.

# Change OverrideAction from Count to None (use rule group's default Block action)
# Update each managed rule group from {"Count": {}} to {"None": {}}
# Monitor CloudWatch metrics for sudden changes in blocked request volume

Key Concepts

Term	Definition
Web ACL	Web Access Control List defining the set of rules evaluated against every HTTP request to a protected resource
Managed Rule Group	Pre-configured rule set maintained by the cloud provider or third-party vendor covering common attack patterns
Rate-Based Rule	WAF rule that tracks request rates per IP address and blocks IPs exceeding the threshold within a time window
Count Mode	WAF action that logs matching requests without blocking them, used for rule validation before enforcement
Rule Priority	Numerical ordering determining which rules are evaluated first; lower numbers have higher priority
Custom Response	WAF capability to return specific HTTP status codes and headers when blocking requests
Scope-Down Statement	Condition that narrows a rate-based rule to specific URI paths, methods, or headers
False Positive	Legitimate request incorrectly blocked by a WAF rule, requiring rule tuning or exclusion

Tools & Systems

AWS WAF: Cloud-native WAF integrated with ALB, CloudFront, API Gateway, and AppSync
Azure WAF: Web application firewall on Application Gateway or Front Door with OWASP CRS rule sets
AWS Firewall Manager: Centralized WAF policy management across multiple AWS accounts in an Organization
WAF Security Automations: AWS solution that deploys Lambda-based automated WAF rule updates based on log analysis
CloudWatch Metrics: Monitoring dashboard for tracking WAF rule match rates, block counts, and allowed requests

Common Scenarios

Scenario: Credential Stuffing Attack Against Authentication API

Context: An e-commerce application experiences 50,000 login attempts per hour from a botnet using stolen credential lists. The attacker rotates source IPs every few minutes to evade simple IP-based blocking.

Approach:

Deploy rate-based rules limiting login endpoint requests to 10 per 5 minutes per IP
Enable AWS WAF Bot Control managed rule group to detect automated request patterns beyond IP rotation
Add a custom rule requiring valid CAPTCHA tokens for login requests exceeding 5 failures
Implement IP reputation blocking using AWSManagedRulesAmazonIpReputationList
Create a custom rule matching on User-Agent patterns common to credential stuffing tools
Monitor blocked request metrics and adjust thresholds based on legitimate traffic patterns

Pitfalls: Setting rate limits too aggressively blocks legitimate users behind shared NAT IPs. Blocking by User-Agent alone is easily bypassed by rotating agent strings.

Output Format

Cloud WAF Configuration Report
================================
Web ACL: production-waf
Scope: Regional (us-east-1)
Protected Resources: ALB (arn:aws:elasticloadbalancing:...)
Report Date: 2025-02-23

RULE CONFIGURATION:
  [P0] RateLimitLogin          - BLOCK (100 req/5min/IP)
  [P1] AWSManagedRulesCommon   - BLOCK (1 exclusion: SizeRestrictions_BODY)
  [P2] AWSManagedRulesSQLi     - BLOCK
  [P3] AWSManagedRulesKnownBad - BLOCK
  [P4] AWSManagedRulesBotControl - COUNT (evaluation phase)
  [P5] GeoBlockRule            - BLOCK (12 countries blocked)

TRAFFIC ANALYSIS (Last 7 Days):
  Total Requests:    2,847,293
  Allowed:           2,791,456 (98.0%)
  Blocked:              51,234 (1.8%)
  Counted:               4,603 (0.2%)

TOP BLOCKED RULES:
  RateLimitLogin:              23,456 blocks (45.8%)
  SQLi Detection:               8,234 blocks (16.1%)
  CommonRuleSet (XSS):          7,891 blocks (15.4%)
  GeoBlockRule:                 6,543 blocks (12.8%)
  KnownBadInputs:              5,110 blocks (10.0%)

FALSE POSITIVE ANALYSIS:
  Reported False Positives: 3
  Confirmed False Positives: 1 (SizeRestrictions_BODY for /api/upload)
  Action Taken: Rule exclusion applied

implementing-cloud-waf-rules