Using the Built-in "Coraza" Web Application Firewall in Tetrate Enterprise Gateway

The Web Application Firewall (WAF) in Tetrate Enterprise Gateway (TEG) examines both inbound and outbound HTTP traffic to identify threats such as attack attempts, malformed traffic, and data exfiltration. By utilizing signature matching, TEG's built-in WAF, powered by Coraza, can block suspicious traffic, issue alerts, and log incidents for further investigation.

Configuration

Coraza is an open-source, high-performance WAF using the widely-accepted mod_security SecLang rules format. It comes pre-configured with the OWASP Core Rule Set (CRS), version 4.3.0 at the time of this writing, which can be customized to fit specific security needs.

Enabling Coraza

Coraza is activated via a Helm configuration. To deploy or update an existing TEG deployment with Coraza enabled, use the following command, adjusting the release name and version as necessary:

helm upgrade --install tetrate-envoy-gateway \
  oci://docker.io/tetrate/teg-envoy-gateway-helm \
  -n envoy-gateway-system --create-namespace \
  --set corazaWaf.enabled=true \
  --version v0.0.0-latest

Verification

To verify Coraza's activation, deploy an example application and attempt a malicious request:

curl -i http://${DEDICATED_GATEWAY_IP}/httpbin/get?arg=<script>alert(0)</script>

A 403 Forbidden response indicates Coraza has successfully identified the request as a potential XSS attack. Further evidence can be found in the gateway's proxy access logs.

Customizing WAF Rules

While the default configuration uses the OWASP CRS, customization is crucial for adapting to specific operational environments to minimize performance impacts and false positives.

Default Configuration

The default Helm values for enabling Coraza are:

values.yaml

corazaWaf:
  enabled: true
  directives:
    - Include @recommended-conf
    - SecRuleEngine On
    - SecDebugLogLevel 2
    - Include @crs-setup-conf
    - Include @owasp_crs/*.conf

Detailed explanations:

• SecRuleEngine On: Activates blocking of detected threats, overriding the more permissive settings from @recommended-conf.
• SecDebugLogLevel 2: Sets the log level to "warning".
• The configuration files (@recommended-conf and @crs-setup-conf) set up the initial rules and operational parameters. The actual rule files (@owasp_crs/*.conf) implement the security measures.

Modifying and Testing New Rules

When modifying rules, the sequence in which directives are listed is crucial; each setting must be strategically placed to ensure proper processing order. Here are steps to fine-tune the WAF behavior:

1. Set Coraza to DetectionOnly mode to non-disruptively observe rule impacts:

   values.yaml

   corazaWaf:
     enabled: true
     directives:
       - Include @recommended-conf
       - SecRuleEngine DetectionOnly
       - SecDebugLogLevel 2
       - Include @crs-setup-conf
       - Include @owasp_crs/*.conf

2. Every log line associated with a triggered rule will contain the string Coraza: Warning. Review the gateway pod logs to identify triggered rules and adjust accordingly to balance security and usability.

3. Once satisfied, switch SecRuleEngine back to On to enforce the rules.

For a detailed guide on rule tuning, refer to the OWASP rule tuning documentation.