[AWS] AWS WAF (Web Application Firewall)

WAF (Web Application Firewall) is a firewall service to protect web applications from common web exploit attacks such as SQL injection or Cross-Site Scripting. You can setup the rules to filter out malicious traffic.

Features

product-page-diagram_AWS-WAF_How-it-Works
https://aws.amazon.com/waf/
  • It is an OSI Layer 7 firewall.
  • It monitors HTTP or HTTPS requests to ELB, CloudFront, or API Gateway.
    • AWS WAF needs to be configured for a specific region if used with ALB or API Gateway, but if used with CloudFront it is configured globally.
  • Blocked traffic returns HTTP 403 (Forbidden) error status.
  • Get real-time metrics and alarms through CloudWatch.

Use Cases

  • Throttle the number of API calls (limit traffic) using rate-based rules
  • Block users – If users generate too many 4xx errors, block traffic from those IPs.
  • Receive notification with unusual traffic

WAF Building Blocks

  • Condition: IP, string, or geo matches; size constraints; SQL injection match; Cross-site scripting match
  • Rule: a group of conditions
  • Web ACL: a group of rules

Web ACL

  • A Web Access Control List (Web ACL) gives you fine-grained control over the web requests.
  • A Web ACL can be associated with Amazon CloudFront, Amazon API Gateway, Application Load Balancer, and AWS AppSync resources.
  • You can re-use a Web ACL across multiple Cloudfront distributions to help reduce costs.

Logging

  • You can send Web ACL logs to
    • CloudWatch Logs
    • S3
    • or Kinesis Data Firehose.

Setting up WAF

You can customize your own rules or use Manged Rules, a preconfigured set of rules managed by AWS or AWS Marketplace Sellers.

WAF can act in 3 ways:

  • Allow all requests except the specified ones (blacklist)
  • Block all requests except the specified ones (whitelist)
  • Count the requests that match the specified conditions

You can specify the following conditions:

  • Source IP address
  • Country of origin
  • Values in request query parameters or headers
  • Length of a request
  • Presence of SQL code that can be malicious (SQL injection)
  • Present of script that can be malicious (Cross-site-scripting)

Rate-base Rules

AWS WAF supports a new rule type – “rate-based” rules.

  • Rate-based rules allow you to configure a rate-based threshold. If, for example, the threshold for the rate-based rule is set to (say) 2,000, the rule will block all IPs that have more than 2,000 requests in the last 5-minute interval.
  • You can create a deny-list of IP addresses that exceed the configured threshold rate (configurable in web requests per trailing 5 minute period).
  • The rule can be used to protect you from use cases such as web-layer DDoS attacks, brute force login attempts and bad bots.

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