Web Application Firewall Infrastructure: A Developer's Guide

Developers have a lot on their plates, juggling feature development, bug fixes, and tight deadlines. Sadly, security often becomes an afterthought instead of a priority integrated from the beginning. However, cyber threats evolve rapidly in today's digital ecosystem, and failure to secure your system can have devastating and long-lasting consequences.

SQL injection, server-side request forgery (SSRF), cross-site scripting (XSS), and distributed denial-of-service (DDoS) attacks continue to be serious threats that can severely compromise application security, expose sensitive data, and disrupt services.

According to a recent Forrester report, 64% of security decision-makers boosted their application budgets to combat the increasing wave of cyberattacks. This shift underscores the pressing need for proactive security solutions and web application firewall (WAF) infrastructure.

The fundamentals: What is a WAF?

A web application firewall infrastructure filters, monitors, and blocks malicious HTTP/S traffic before it reaches your application, preventing threats like SQL injection, XSS, and WAF bypass.

Unlike traditional firewalls that operate at network levels (Layers 3 and 4 of the OSI model), WAFs function at the application layer (Layer 7). This feature allows them to recognize and neutralize web-specific attacks that conventional firewalls might overlook, ensuring your application stays protected from evolving security threats.

Key Differences: Blocklist vs. Allowlist WAFs

A blocklist WAF blocks traffic identified as malicious based on known attack patterns, making it effective against threats like SQL injection, XSS, and bot attacks. However, it needs constant updates to stay relevant.

An allowlist WAF takes a stricter approach, allowing only predefined safe traffic. While offering higher security for sensitive applications, it requires meticulous setup and maintenance to prevent legitimate users from being blocked.

A blocklist WAF is easier to deploy but relies on frequent updates to stay ahead of threats. An allowlist WAF, though more secure, requires extensive tuning to avoid blocking legitimate traffic. Understanding the nuances of blocklist and allowlist approaches is essential when configuring effective WAF rules.

Types of Web Application Firewall Infrastructure

When it comes to protecting web applications, one size does not fit all. You can choose between network-based, host-based, and cloud-based WAFs depending on your infrastructure, performance needs, and security priorities. Each type has its own advantages and trade-offs, making them suitable for different deployment scenarios.

1. Network-Based WAFs

Network-based WAFs are installed on an organization's network infrastructure, usually as hardware appliances or virtual machines. Deployed at the network's perimeter, they analyze all incoming and outgoing web traffic before it makes its way to the application server. Effective deployment and management of network-based WAFs require a comprehensive understanding of your infrastructure, highlighting the need for robust asset management.

Advantages: Low latency, high-speed filtering, and robust security for on-premises applications.
Challenges: Needs dedicated infrastructures, continuous maintenance, and higher upfront costs.
Best for: On-premise data centers for enterprises that require high-performance security.

2. Host-Based WAFs

Host-based WAFs are installed directly on the application server and integrated closely with the environment in which they are hosted. This type of WAF enables fine-grained security configurations and greater visibility of application-layer traffic.

Advantages: Customizable security policies, more in-depth traffic inspection, and less organizational reliance on external hardware.
Challenges: Consumes server resources, potentially impacting application performance. Requires ongoing maintenance.
Best for: Organizations needing granular security control over individual applications.

3. Cloud-Based WAFs

These WAFs are hosted and offered as a service on the cloud. They are owned and maintained by third-party providers and offer automated updates and threat intelligence.

Advantages: Easy deployment, automatic updates, scalability, and lower maintenance costs.
Challenges: Less control over security policies and potential reliance on third-party providers.
Best for: Businesses with cloud-hosted applications seeking scalable, hassle-free security.

Each type of WAF offers unique benefits depending on an organization's infrastructure and security requirements. Many modern businesses opt for cloud-based WAFs due to their flexibility, while enterprises with dedicated security teams may prefer network-based or host-based solutions for greater control.

5 Ways Web Application Firewall Infrastructure is Critical for Security

A well-implemented web application firewall infrastructure is essential for safeguarding web applications against ever-evolving threats. Here are five key reasons why a WAF is crucial for modern security:

1. Protection Against Common Web Exploits

Web applications are prime targets for threats like SQL injection, cross-site scripting (XSS), and cross-site request forgery (CSRF). A WAF acts as a frontline defense, filtering out malicious payloads before they can exploit vulnerabilities like the OWASP Top 10.

Example: If an attacker tries to extract sensitive user data from a database via SQL injection, a WAF can mitigate this attack by blocking the malicious traffic.

2. DDoS Mitigation

Web DDoS attacks are also one of the most common types of attacks. They overload web applications with excessive traffic and cause downtime and service disruption. A WAF prevents this by monitoring incoming traffic and blocking suspicious patterns.

Example: Consider an eCommerce website that suddenly receives high traffic over multiple requests from unfamiliar locations. A WAF can filter out these malicious requests based on request location and prevent the server from overloading.

3. Bot Mitigation

Malicious bots are responsible for many web-based attacks, including credential stuffing, web scraping, and automated exploitation attempts. WAFs use advanced algorithms to differentiate between legitimate users and harmful bots.

Example: A ticketing platform can prevent bots from scalping event tickets by using a WAF to identify and block automated purchasing scripts.

4. Compliance with Security Standards

Regulatory compliance is a major concern for businesses working with sensitive data. WAFs help organizations comply with security requirements for standards such as PCI DSS, GDPR, and HIPAA by enforcing strict access controls and logging security events.

Example: A financial services organization processing credit card transactions can deploy a WAF to prevent unauthorized access attempts and ensure that it is PCI DSS compliant.

5. Securing APIs and Web Applications

As APIs are essential for modern applications, securing API endpoints is critical. WAFs perform deep inspection of API traffic, preventing unauthorized requests and injection attacks.

Example: If your SaaS platform integrates with third-party services through APIs, a WAF can be deployed to detect and prevent API abuse from unauthorized sources.

6 Key Features of a Secure Web Application Firewall Infrastructure

A well-designed WAF should do more than just block threats. It should proactively identify risks, adapt to emerging attack patterns, and ensure seamless security integration. Here are six must-have features that define a robust WAF:

1. Preemptive Threat Prevention

A great WAF doesn't just block known threats. It stops attacks before they even emerge, analyzing user behavior and request patterns detects and neutralizes risks in real time.

Example: A financial services platform can prevent credential stuffing attacks by identifying and blocking unusual login attempts before they succeed.

2. Machine Learning-based Security

Traditional signature-based security is outdated. Modern WAFs leverage machine learning (ML) to identify anomalies, detect zero-day threats, and continuously improve accuracy.

Example: A blog can prevent content scraping using ML algorithms that distinguish between legitimate users and automated crawlers.

3. API Discovery & Protection

WAFs with API discovery capabilities help detect rogue APIs, validate schemas, and block malicious API traffic before it causes harm.

Example: A fintech app can prevent unauthorized API calls by validating requests against an approved schema before processing them.

4. Intrusion Prevention System (IPS)

A WAF with intrusion prevention functionality can identify and mitigate vulnerabilities before they are exploited. For example, open-appsec protects against over 2,800 known web vulnerabilities, making it an essential security layer.

Example: A SaaS platform that blocks attackers from exploiting outdated third-party libraries by proactively identifying risky traffic patterns.

5. Advanced Anti-bot Measures

Bots can brute-force passwords, scrape data, and carry out fraudulent transactions. Therefore, highly reliable web application firewall infrastructure can distinguish between good and bad bots, protecting your application without sacrificing user experience.

6. Zero-day Threat Protection

Signature-based WAFs struggle with new threats, but advanced solutions offer zero-day protection by leveraging ML-based analysis. open-appsec is a great example. It was the only WAF that blocked Log4Shell, Text4Shell, and Spring4Shell attacks preemptively without needing signatures. Hence, a well-equipped WAF should go beyond just filtering traffic. It should actively learn, adapt, and defend against evolving threats to keep your applications secure.

open-appsec is an open-source project that builds on machine learning to provide pre-emptive web app & API threat protection against OWASP Top 10 and zero-day attacks. It simplifies maintenance as there is no threat signature upkeep and exception handling, like common in many WAF solutions.

To learn more about how open-appsec works, see this White Paper and the in-depth Video Tutorial. You can also experiment with deployment in the free Playground.