Securing API Gateway With AWS Waf

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).

Common Misconfigurations & Verification

• Web ACL created but never associated protects nothing. Confirm attachment with aws wafv2 get-web-acl-for-resource --resource-arn arn:aws:apigateway:REGION::/restapis/API_ID/stages/prod. API Gateway requires --scope REGIONAL; a CLOUDFRONT-scope ACL will not attach.
• Rules left in Count / OverrideAction: Count log but never block. Verify the intended managed groups and custom rules show Action: Block in get-web-acl, not Count.
• Rate-based window misunderstanding: RateBasedStatement Limit is requests per trailing 5-minute window aggregated per source IP (5-min minimum), so 2000 is not per-minute. Clients behind shared NAT share a key. Confirm blocking with get-rate-based-statement-managed-keys.
• Scope-down match misses: a ByteMatchStatement on /api/auth/login with LOWERCASE won't match URL-encoded or case-sensitive upstream paths. Body inspection only covers the first 8 KB unless SizeConstraintStatement uses OversizeHandling: MATCH.
• "Require x-api-key" is not auth: the NotStatement + PositionalConstraint: EXACTLY empty-string pattern blocks missing/empty headers but allows any wrong key.

Verify it actually works: send a known SQLi/XSS payload and confirm a 403 appears in aws wafv2 get-sampled-requests --rule-metric-name ...; flood the login path and confirm RateLimitLogin blocks; and confirm logging is on via get-logging-configuration (otherwise blocks aren't auditable). Start new rules in Count, review samples, then flip to Block.

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

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%