Introduction to Application Gateway Security

Azure Application Gateway provides robust security features to protect your web applications from common exploits and threats. It acts as a Layer 7 load balancer, offering capabilities like Web Application Firewall (WAF), SSL/TLS termination, and more, all designed to enhance your application's security posture.

This documentation explores the various security aspects of Azure Application Gateway, helping you configure and manage a secure environment for your deployed applications.

Key Security Features

Azure Application Gateway offers a suite of integrated security features:

  • Web Application Firewall (WAF): Protects against OWASP Top 10 vulnerabilities.
  • SSL/TLS Termination: Encrypts and decrypts traffic, offloading this task from your backend servers.
  • End-to-End SSL/TLS Encryption: Ensures data remains encrypted throughout its journey.
  • Network Security Groups (NSGs): Controls inbound and outbound traffic to your Application Gateway.
  • Azure Private Link: Enables secure access to your Application Gateway from your virtual network.
  • Cookie-based Session Affinity: Helps in maintaining user sessions securely.
  • URL-based Content Routing: Allows for granular traffic management based on URLs.

Web Application Firewall (WAF)

The Web Application Firewall (WAF) for Azure Application Gateway is a crucial component for protecting your web applications. It helps protect your applications from common web vulnerabilities like SQL injection, cross-site scripting (XSS), and other exploits detected by the OWASP core rule sets.

WAF Modes

  • Detection Mode: WAF logs malicious requests but doesn't block them. This is useful for monitoring and tuning.
  • Prevention Mode: WAF blocks malicious requests and logs them, actively protecting your application.

WAF Policies

You can create custom WAF policies to define rulesets, managed rules, and exclusions tailored to your application's needs.


# Example WAF policy configuration (conceptual)
{
  "name": "MyWAFPolicy",
  "mode": "Prevention",
  "managedRules": {
    "ruleSets": [
      {
        "ruleSetType": "OWASP",
        "ruleSetVersion": "3.2"
      }
    ],
    "exclusions": [
      {
        "matchVariable": "RequestUri",
        "selector": "POST /user/profile"
      }
    ]
  }
}

SSL/TLS Termination

Application Gateway can terminate SSL/TLS connections, which means it decrypts incoming traffic before forwarding it to your backend servers. This simplifies certificate management and reduces the load on your backend infrastructure.

Configuring SSL Certificates

You can upload your own SSL certificates or use certificates stored in Azure Key Vault. Application Gateway supports both PFX and PEM certificate formats.

End-to-End SSL/TLS Encryption

For enhanced security, you can configure Application Gateway to perform end-to-end SSL/TLS encryption. In this scenario, Application Gateway encrypts the traffic again before sending it to the backend servers, ensuring data remains encrypted throughout its journey. This requires backend servers to have valid SSL certificates as well.

Network Security Groups (NSGs)

Network Security Groups (NSGs) can be associated with the subnet where your Application Gateway resides. They act as a firewall at the network level, allowing or denying traffic based on source/destination IP addresses, ports, and protocols.

It's recommended to configure NSGs to allow traffic only from trusted sources to your Application Gateway's public IP address on common web ports (80 and 443).

Access Control

Azure Role-Based Access Control (RBAC) should be used to manage who can configure and manage your Application Gateway resources. Grant permissions based on the principle of least privilege to ensure only authorized personnel can make changes.

Advanced Threat Protection

In addition to WAF, consider integrating Application Gateway with other Azure security services like Azure Sentinel for advanced threat detection and incident response, and Azure Security Center for unified security management and threat protection.

Security Best Practices

  • Always enable the WAF in prevention mode for production environments.
  • Keep WAF managed rule sets updated to the latest versions.
  • Configure SSL/TLS certificates with strong encryption and renew them before expiration.
  • Use end-to-end SSL/TLS encryption when sensitive data is transmitted.
  • Restrict access to your Application Gateway using NSGs and Azure Firewall.
  • Utilize Azure Private Link for secure, private access.
  • Regularly review WAF logs and audit trails for suspicious activity.
  • Implement a robust certificate management strategy.
  • Configure health probes carefully to ensure traffic is only sent to healthy backend instances.