Securing API Gateway with AWS WAF

When to Use

• When deploying API Gateway endpoints that require protection against common web attacks
• When implementing rate limiting and throttling to prevent API abuse and DDoS attacks
• When building bot detection and mitigation for API endpoints exposed to the internet
• When compliance requires WAF protection for all public-facing API endpoints
• When customizing access controls based on IP reputation, geolocation, or request patterns

Do not use for network-level DDoS protection (use AWS Shield), for application logic vulnerabilities (use SAST/DAST tools), or for internal API security between microservices (use service mesh authentication and authorization).

Prerequisites

• AWS API Gateway (REST or HTTP API) deployed with public endpoints
• IAM permissions for wafv2:* and apigateway:* operations
• CloudWatch and S3 or Kinesis Firehose configured for WAF logging
• Understanding of the API's expected traffic patterns for rate limiting configuration
• IP reputation lists or threat intelligence feeds for custom IP blocking

Workflow

Step 1: Create a WAF Web ACL with Managed Rule Groups

Create a Web ACL with AWS Managed Rules for baseline protection against OWASP Top 10 attacks.

# Create a WAF Web ACL with managed rule groups
aws wafv2 create-web-acl \
  --name api-gateway-waf \
  --scope REGIONAL \
  --default-action '{"Allow":{}}' \
  --visibility-config '{
    "SampledRequestsEnabled": true,
    "CloudWatchMetricsEnabled": true,
    "MetricName": "api-gateway-waf"
  }' \
  --rules '[
    {
      "Name": "AWSManagedRulesCommonRuleSet",
      "Priority": 1,
      "Statement": {
        "ManagedRuleGroupStatement": {
          "VendorName": "AWS",
          "Name": "AWSManagedRulesCommonRuleSet"
        }
      },
      "OverrideAction": {"None": {}},
      "VisibilityConfig": {
        "SampledRequestsEnabled": true,
        "CloudWatchMetricsEnabled": true,
        "MetricName": "CommonRuleSet"
      }
    },
    {
      "Name": "AWSManagedRulesKnownBadInputsRuleSet",
      "Priority": 2,
      "Statement": {
        "ManagedRuleGroupStatement": {
          "VendorName": "AWS",
          "Name": "AWSManagedRulesKnownBadInputsRuleSet"
        }
      },
      "OverrideAction": {"None": {}},
      "VisibilityConfig": {
        "SampledRequestsEnabled": true,
        "CloudWatchMetricsEnabled": true,
        "MetricName": "KnownBadInputs"
      }
    },
    {
      "Name": "AWSManagedRulesSQLiRuleSet",
      "Priority": 3,
      "Statement": {
        "ManagedRuleGroupStatement": {
          "VendorName": "AWS",
          "Name": "AWSManagedRulesSQLiRuleSet"
        }
      },
      "OverrideAction": {"None": {}},
      "VisibilityConfig": {
        "SampledRequestsEnabled": true,
        "CloudWatchMetricsEnabled": true,
        "MetricName": "SQLiRuleSet"
      }
    },
    {
      "Name": "AWSManagedRulesAmazonIpReputationList",
      "Priority": 4,
      "Statement": {
        "ManagedRuleGroupStatement": {
          "VendorName": "AWS",
          "Name": "AWSManagedRulesAmazonIpReputationList"
        }
      },
      "OverrideAction": {"None": {}},
      "VisibilityConfig": {
        "SampledRequestsEnabled": true,
        "CloudWatchMetricsEnabled": true,
        "MetricName": "IPReputationList"
      }
    }
  ]'

Step 2: Add Rate Limiting Rules

Configure rate-based rules to throttle excessive API requests per IP address.

# Get the Web ACL ARN and lock token
WEB_ACL_ARN=$(aws wafv2 list-web-acls --scope REGIONAL \
  --query "WebACLs[?Name=='api-gateway-waf'].ARN" --output text)

# Update Web ACL to add rate limiting rule
aws wafv2 update-web-acl \
  --name api-gateway-waf \
  --scope REGIONAL \
  --id $(aws wafv2 list-web-acls --scope REGIONAL --query "WebACLs[?Name=='api-gateway-waf'].Id" --output text) \
  --lock-token $(aws wafv2 get-web-acl --name api-gateway-waf --scope REGIONAL --id WEB_ACL_ID --query 'LockToken' --output text) \
  --default-action '{"Allow":{}}' \
  --visibility-config '{
    "SampledRequestsEnabled": true,
    "CloudWatchMetricsEnabled": true,
    "MetricName": "api-gateway-waf"
  }' \
  --rules '[
    {
      "Name": "RateLimitPerIP",
      "Priority": 0,
      "Statement": {
        "RateBasedStatement": {
          "Limit": 2000,
          "AggregateKeyType": "IP"
        }
      },
      "Action": {"Block": {}},
      "VisibilityConfig": {
        "SampledRequestsEnabled": true,
        "CloudWatchMetricsEnabled": true,
        "MetricName": "RateLimitPerIP"
      }
    },
    {
      "Name": "RateLimitLoginEndpoint",
      "Priority": 5,
      "Statement": {
        "RateBasedStatement": {
          "Limit": 100,
          "AggregateKeyType": "IP",
          "ScopeDownStatement": {
            "ByteMatchStatement": {
              "FieldToMatch": {"UriPath": {}},
              "PositionalConstraint": "STARTS_WITH",
              "SearchString": "/api/auth/login",
              "TextTransformations": [{"Priority": 0, "Type": "LOWERCASE"}]
            }
          }
        }
      },
      "Action": {"Block": {}},
      "VisibilityConfig": {
        "SampledRequestsEnabled": true,
        "CloudWatchMetricsEnabled": true,
        "MetricName": "RateLimitLogin"
      }
    }
  ]'

Step 3: Implement Bot Control

Add AWS WAF Bot Control to detect and manage automated traffic.

# Add Bot Control managed rule group
# (Add to the rules array when updating the Web ACL)
{
  "Name": "AWSManagedRulesBotControlRuleSet",
  "Priority": 6,
  "Statement": {
    "ManagedRuleGroupStatement": {
      "VendorName": "AWS",
      "Name": "AWSManagedRulesBotControlRuleSet",
      "ManagedRuleGroupConfigs": [{
        "AWSManagedRulesBotControlRuleSet": {
          "InspectionLevel": "COMMON"
        }
      }],
      "ExcludedRules": [
        {"Name": "CategoryHttpLibrary"},
        {"Name": "SignalNonBrowserUserAgent"}
      ]
    }
  },
  "OverrideAction": {"None": {}},
  "VisibilityConfig": {
    "SampledRequestsEnabled": true,
    "CloudWatchMetricsEnabled": true,
    "MetricName": "BotControl"
  }
}

Step 4: Create Custom Rules for API-Specific Protection

Build custom WAF rules for API-specific security requirements.

# Block requests without required API key header
{
  "Name": "RequireAPIKey",
  "Priority": 7,
  "Statement": {
    "NotStatement": {
      "Statement": {
        "ByteMatchStatement": {
          "FieldToMatch": {
            "SingleHeader": {"Name": "x-api-key"}
          },
          "PositionalConstraint": "EXACTLY",
          "SearchString": "",
          "TextTransformations": [{"Priority": 0, "Type": "NONE"}]
        }
      }
    }
  },
  "Action": {"Block": {"CustomResponse": {"ResponseCode": 403}}},
  "VisibilityConfig": {
    "SampledRequestsEnabled": true,
    "CloudWatchMetricsEnabled": true,
    "MetricName": "RequireAPIKey"
  }
}

# Geo-restrict to allowed countries
{
  "Name": "GeoRestriction",
  "Priority": 8,
  "Statement": {
    "NotStatement": {
      "Statement": {
        "GeoMatchStatement": {
          "CountryCodes": ["US", "CA", "GB", "DE", "FR", "AU"]
        }
      }
    }
  },
  "Action": {"Block": {}},
  "VisibilityConfig": {
    "SampledRequestsEnabled": true,
    "CloudWatchMetricsEnabled": true,
    "MetricName": "GeoRestriction"
  }
}

# Block oversized request bodies (prevent payload attacks)
{
  "Name": "MaxBodySize",
  "Priority": 9,
  "Statement": {
    "SizeConstraintStatement": {
      "FieldToMatch": {"Body": {"OversizeHandling": "MATCH"}},
      "ComparisonOperator": "GT",
      "Size": 10240,
      "TextTransformations": [{"Priority": 0, "Type": "NONE"}]
    }
  },
  "Action": {"Block": {}},
  "VisibilityConfig": {
    "SampledRequestsEnabled": true,
    "CloudWatchMetricsEnabled": true,
    "MetricName": "MaxBodySize"
  }
}

Step 5: Associate WAF with API Gateway and Enable Logging

Attach the Web ACL to the API Gateway stage and configure comprehensive logging.

# Associate Web ACL with API Gateway
aws wafv2 associate-web-acl \
  --web-acl-arn $WEB_ACL_ARN \
  --resource-arn arn:aws:apigateway:us-east-1::/restapis/API_ID/stages/prod

# Enable WAF logging to S3 via Kinesis Firehose
aws wafv2 put-logging-configuration \
  --logging-configuration '{
    "ResourceArn": "'$WEB_ACL_ARN'",
    "LogDestinationConfigs": [
      "arn:aws:firehose:us-east-1:ACCOUNT:deliverystream/aws-waf-logs-api-gateway"
    ],
    "RedactedFields": [
      {"SingleHeader": {"Name": "authorization"}},
      {"SingleHeader": {"Name": "cookie"}}
    ]
  }'

# Verify association
aws wafv2 get-web-acl-for-resource \
  --resource-arn arn:aws:apigateway:us-east-1::/restapis/API_ID/stages/prod

Step 6: Monitor WAF Metrics and Tune Rules

Monitor WAF effectiveness and tune rules to reduce false positives.

# Get WAF metrics from CloudWatch
aws cloudwatch get-metric-statistics \
  --namespace AWS/WAFV2 \
  --metric-name BlockedRequests \
  --dimensions Name=WebACL,Value=api-gateway-waf Name=Rule,Value=ALL \
  --start-time 2026-02-22T00:00:00Z \
  --end-time 2026-02-23T00:00:00Z \
  --period 3600 \
  --statistics Sum

# Get sampled requests for a specific rule
aws wafv2 get-sampled-requests \
  --web-acl-arn $WEB_ACL_ARN \
  --rule-metric-name RateLimitPerIP \
  --scope REGIONAL \
  --time-window '{"StartTime":"2026-02-22T00:00:00Z","EndTime":"2026-02-23T00:00:00Z"}' \
  --max-items 50

# Check rate-limited IPs
aws wafv2 get-rate-based-statement-managed-keys \
  --web-acl-name api-gateway-waf \
  --scope REGIONAL \
  --web-acl-id WEB_ACL_ID \
  --rule-name RateLimitPerIP

# Create CloudWatch alarm for high block rate
aws cloudwatch put-metric-alarm \
  --alarm-name waf-high-block-rate \
  --namespace AWS/WAFV2 \
  --metric-name BlockedRequests \
  --dimensions Name=WebACL,Value=api-gateway-waf Name=Rule,Value=ALL \
  --statistic Sum --period 300 --threshold 1000 \
  --comparison-operator GreaterThanThreshold \
  --evaluation-periods 2 \
  --alarm-actions arn:aws:sns:us-east-1:ACCOUNT:security-alerts

Key Concepts

Term	Definition
Web ACL	AWS WAF access control list that defines the collection of rules and their actions (allow, block, count) applied to associated resources
Managed Rule Group	Pre-configured set of WAF rules maintained by AWS or third-party vendors for common attack patterns like OWASP Top 10
Rate-Based Rule	WAF rule that tracks request rates per IP address and blocks traffic exceeding a defined threshold within a 5-minute window
Bot Control	AWS WAF managed rule group that identifies and manages automated traffic including scrapers, crawlers, and attack bots
IP Reputation List	AWS-maintained list of IP addresses associated with malicious activity including botnets, scanners, and known attackers
Custom Response	WAF capability to return specific HTTP status codes and custom response bodies when blocking requests

Tools & Systems

• AWS WAF: Web application firewall service for protecting API Gateway, ALB, CloudFront, and AppSync endpoints
• AWS Managed Rules: Pre-built rule groups for common attack patterns maintained by AWS security team
• AWS Firewall Manager: Central management of WAF policies across multiple accounts in AWS Organizations
• Kinesis Firehose: Streaming delivery service for WAF logs to S3, Elasticsearch, or third-party analytics
• CloudWatch: Monitoring service for WAF metrics including allowed, blocked, and counted requests

Common Scenarios

Scenario: Protecting a Public API from Credential Stuffing and Bot Attacks

Context: A public REST API experiences thousands of authentication attempts per hour from automated bots attempting credential stuffing against the /api/auth/login endpoint.

Approach:

1. Create a Web ACL with AWS Managed Rules Common Rule Set for baseline protection
2. Add a rate-based rule limiting the login endpoint to 100 requests per IP per 5 minutes
3. Enable Bot Control managed rules to detect and block automated traffic
4. Add IP Reputation List to block known malicious IPs proactively
5. Create a custom rule blocking requests without proper User-Agent headers
6. Enable WAF logging and create CloudWatch alarms for high block rates
7. Review sampled blocked requests weekly to tune rules and reduce false positives

Pitfalls: Rate limiting by IP can block legitimate users behind shared NAT gateways or corporate proxies. Consider using API key or authenticated session-based rate limiting for more granular control. Bot Control rules in COMMON inspection level may block legitimate API clients; start in Count mode and review before switching to Block.

Output Format

AWS WAF API Gateway Security Report
======================================
Web ACL: api-gateway-waf
Associated Resource: API Gateway - production-api (prod stage)
Report Period: 2026-02-16 to 2026-02-23

TRAFFIC SUMMARY:
  Total requests:              2,450,000
  Allowed requests:            2,380,000 (97.1%)
  Blocked requests:               70,000 (2.9%)

BLOCKS BY RULE:
  RateLimitPerIP:              28,000 (40%)
  AWSManagedRulesCommonRuleSet: 18,000 (25.7%)
  BotControl:                  12,000 (17.1%)
  SQLiRuleSet:                  5,000 (7.1%)
  IPReputationList:             4,000 (5.7%)
  RateLimitLogin:               2,000 (2.9%)
  GeoRestriction:               1,000 (1.4%)

TOP BLOCKED IPs:
  185.x.x.x:     8,400 requests (rate limited)
  45.x.x.x:      5,200 requests (bot detected)
  198.x.x.x:     3,100 requests (SQLi attempts)

ATTACK TYPES BLOCKED:
  Credential stuffing (login endpoint):  2,000
  SQL injection attempts:                5,000
  Cross-site scripting:                  3,200
  Known bad bot traffic:                12,000
  Rate limit violations:               28,000

WAF RULE HEALTH:
  Rules in Block mode:    8 / 10
  Rules in Count mode:    2 / 10 (under evaluation)
  False positive rate:    < 0.1%