Infosec Journey

Web Application Firewalls (WAFs) have become a cornerstone of modern network and perimeter security. Not only are they a best practice for protecting web applications, but some regulations—such as PCI DSS—now mandate their use. As the threat landscape evolves and compliance demands increase, WAF deployment and licensing models have also matured, providing organizations with the flexibility to manage costs (CAPEX vs. OPEX) and risk.

A Web Application Firewall operates at Layer 7 of the OSI model. It filters and monitors HTTP/HTTPS traffic to block malicious attacks, especially those listed in the OWASP Top 10. These attacks include SQL injection and cross-site scripting (XSS). By acting as a reverse proxy, a WAF inspects incoming requests. It applies security rules. It forwards only safe traffic to the web application server.

Deployment Models: On-Premises vs. Cloud

On-Premises WAF

How it works:
You install a physical or virtual WAF appliance. Place it inside your own data center. Usually, it’s positioned right in front of your web servers. All incoming traffic flows through this device, where it’s inspected and (if necessary) blocked in real time.

Why choose on-prem?

• Total control: You manage the hardware, software, and all security policies.
• Customization: Deeply tune rules, logs, and integrate with your SIEM.
• Compliance: Perfect for strict requirements (GDPR, PCI DSS, data residency).
• Low latency: Local processing is ideal for real-time or high-frequency apps.

Licensing:
Usually a one-time purchase (CAPEX) with ongoing support and maintenance.

Cloud-Based WAF

How it works:
A third-party provider hosts the WAF in the cloud. You redirect your web traffic (usually via DNS) to their network, where it’s filtered before reaching your servers. Most cloud WAFs decrypt HTTPS traffic to inspect everything—headers, URLs, cookies, even payloads—then re-encrypt before sending it on.

Why choose cloud?

• Scalability: Instantly handle traffic spikes—no hardware limits.
• Global reach: Providers have points of presence worldwide for low-latency protection.
• DDoS defense: Massive, distributed infrastructure shrugs off big attacks.
• Hands-off maintenance: The provider patches, updates, and manages threat intelligence.

Licensing:
Subscription or pay-as-you-go (OPEX), so costs are predictable and scale with usage.

Security Features You Should Expect

Whether on-prem or in the cloud, modern WAFs offer:

• SSL/TLS Inspection: Decrypt and inspect encrypted traffic.
• Mutual TLS (mTLS): Especially for secure connections between cloud WAFs and your servers.
• Bot Management: Block malicious bots and scrapers.
• IP Reputation Filtering: Stop known bad actors.
• Rate Limiting: Thwart brute-force and DDoS attacks.
• SIEM Integration: For real-time monitoring and incident response.

Real-World Incidents: The Cost of Misconfiguration

Misconfiguration can undermine even the best WAF deployments:

• Cloud WAF Example: In a high-profile incident, a major US bank suffered a breach affecting 106 million customers. This occurred when a misconfigured cloud WAF allowed an attacker to exploit a Server-Side Request Forgery (SSRF) vulnerability. The attacker accessed AWS metadata, obtained credentials, and compromised sensitive data stored in S3.
• On-Prem WAF Example: While less often publicized, financial and insurance companies have experienced downtime. They have also faced data loss due to misconfigured or overly aggressive on-prem WAF rules. This highlights the need for careful configuration and monitoring.

WAF Trends: What’s Next?

WAF technology is rapidly advancing to address new threats and business needs:

• AI and Machine Learning: Modern WAFs use ML to detect anomalous traffic and adapt to evolving attack patterns.
• API Security: With APIs as a primary attack vector, WAFs now offer schema validation, rate limiting, and endpoint-specific rules.
• Zero Trust Integration: WAFs are critical enforcement points for Zero Trust. They require identity verification and continuous access validation. They often integrate with IAM systems for token and MFA enforcement.
• Behavioral Analytics: Advanced WAFs monitor user and application behavior to detect subtle threats.
• Managed Services: Cloud-based WAFs offer automated updates and threat intelligence, reducing operational overhead.

Example: Zero Trust with WAF

A Zero Trust-aligned WAF might require all requests to sensitive endpoints (e.g., /admin, /api/transfer) to include a valid, signed authentication token from the IAM system. If the session is expired or the token is invalid, the WAF blocks the request before it reaches the application. For high-risk actions, the WAF may enforce recent MFA validation.

Final Thoughts

WAFs are now essential for any organization running web applications.
On-premises WAFs give you control and compliance, ideal for regulated or latency-sensitive environments.
Cloud-based WAFs offer scalability, global protection, and simplicity—great for fast-moving, distributed businesses.

No matter if you go on-prem or cloud, staying ahead means keeping your WAF updated, tested, and closely monitored. These tools bring the power. It’s up to us to fine-tune and manage them smartly. This is essential to keep our apps secure in today’s fast-evolving threat landscape.