What is a Web Application Firewall (WAF)?
A Web application firewall (WAF) is a security system that protects web applications by filtering, monitoring, and blocking malicious HTTP/S traffic. Unlike traditional firewalls that focus on network traffic, WAFs operate at the application layer, analyzing web requests for common attacks such as SQL injection, cross-site scripting (XSS), and other vulnerabilities defined in the OWASP Top 10.
This allows organizations to protect sensitive customer data, ensure application availability, and maintain regulatory compliance. WAFs are deployed either as hardware appliances, virtual appliances, or cloud-based services positioned in front of web servers.
They act as an intermediary between the user and the web application, inspecting bidirectional web-based traffic and applying predefined security rules. These solutions block attacks and provide logging, alerting, and learning capabilities to adapt to new threats.
In this article:
Zero-Day Threat Prevention and Virtual Patching
Zero-day threats exploit vulnerabilities that are unknown to the application vendor and do not yet have a security patch available. WAFs deliver protection against these attacks through behavioral analysis, signature-based detection, and virtual patching. Virtual patching applies mitigating controls at the WAF layer to block attack vectors targeting vulnerable application components, reducing the risk window while an official patch is in development or rollout.
Enterprises benefit from virtual patching as it significantly reduces the time and operational complexity associated with patching critical web applications, especially in large, distributed environments. Manual patching may require extensive regression testing or downtime, so virtual patches provide continuity of service while maintaining security controls.
AI-Driven Detection
Modern WAFs increasingly leverage artificial intelligence (AI) and machine learning (ML) technologies to identify novel threats and detect sophisticated attack patterns that bypass traditional signature-based defenses. These systems analyze historical and real-time traffic data to establish baselines of “normal” application behavior. Any anomalies, such as irregular request rates or unusual data patterns, are flagged as potential threats.
By continuously learning from the environment, AI-powered WAFs decrease false positives and adapt to evolving attack techniques without extensive manual tuning. Enterprises gain the advantage of adaptive security that can keep pace with rapid changes in the threat landscape, ensuring up-to-date protection with minimal administrative overhead.
Modern API Support
With the rapid adoption of cloud-native architectures and microservices, APIs are now a fundamental part of enterprise applications. Modern WAFs extend their inspection capabilities to protect APIs against threats such as parameter tampering, authentication bypass, and excessive data exposure. These solutions understand REST, GraphQL, and other API protocols, enabling automatic security rule creation and enforcement tailored to API endpoints.
API protection also includes tracking usage quotas, enforcing user authentication, and monitoring for abnormal usage behaviors—features not typically provided by traditional WAFs. Ensuring API security at the WAF layer enables enterprises to control access, prevent abuse, and comply with privacy regulations as applications become more modular and interconnected.
Elastic, Multi-Tenant Architecture
Scalability and multi-tenancy are core requirements for enterprise WAF solutions, especially when supporting diverse business units, customers, or applications hosted in the cloud. An elastic WAF architecture enables dynamic scaling of resources to handle traffic spikes or growth, ensuring performance is not degraded during periods of high demand.
Multi-tenant support allows administrators to manage security policies, logging, and reporting for segregated environments from a unified interface. This architecture makes it possible to serve multiple departments or customers while maintaining isolation of data and configuration.
Learn more in our detailed guide to web application firewall architecture.
DevSecOps and CI/CD Integration
Effective enterprise WAFs integrate smoothly with DevSecOps practices and CI/CD (continuous integration/continuous deployment) workflows. This integration allows security policies to be versioned, tested, and deployed alongside application code, significantly reducing the gap between development and security. By embedding WAF policy updates into CI/CD pipelines, organizations ensure new vulnerabilities are addressed before code is pushed to production.
Automated integration also fosters greater collaboration between development, operations, and security teams. Security checks can be performed early in the development lifecycle, preventing common misconfigurations or exposures from reaching end users.
Compliance Support
Regulatory compliance is a top priority for enterprises managing sensitive or regulated data. WAF solutions often include features that support compliance with standards such as PCI DSS, GDPR, HIPAA, and others. These features may involve logging and auditing, customizable reporting, and automated rule sets aligned with regulatory requirements.
By providing audit-ready logs and security analytics, WAFs simplify the process of demonstrating compliance to auditors or regulators. Beyond reporting, compliance-aligned policies in WAFs help enterprises enforce data leakage prevention, secure credit card information, and ensure privacy controls are in place.
Radware Cloud WAF is a cloud-native web application firewall that protects applications and APIs from a broad spectrum of web threats, including OWASP Top 10 vulnerabilities, bot attacks, and data leakage. Delivered as part of Radware’s Cloud Application Protection Service, it combines machine learning, advanced threat intelligence, and automation to provide continuous, adaptive protection with minimal manual effort.
Key features include:
- Automated rule generation: Analyzes applications and automatically creates precise security policies to detect and block threats without overblocking.
- Threat intelligence–driven defense: Leverages global attack data to identify and mitigate emerging vulnerabilities and exploit patterns in real time.
- Bot and API protection: Uses device fingerprinting and AI-powered API discovery to prevent abuse from malicious bots and unauthorized API usage.
- Data leak prevention: Blocks transmission of sensitive data such as credentials, credit card numbers, and personal identifiers.
- Compliance and certifications: NSS Labs recommended, ICSA Labs certified, and PCI-DSS compliant for robust enterprise-grade security.
- Integrated Layer-7 protection: Includes web DDoS mitigation and client-side protection for a full-stack security approach.
Fortinet FortiWeb is a web application firewall that protects web applications and APIs from a range of threats, including those listed in the OWASP Top 10, zero-day vulnerabilities, and automated bot attacks. It uses a dual-layer machine learning engine to detect and respond to anomalies, reducing false positives and administrative workload.
General features include:
- Protects web applications and APIs against OWASP Top-10, DDoS, and bot attacks
- Dual-layer machine learning for behavioral anomaly detection and false positive reduction
- Automatic API discovery and schema-based protection (OpenAPI, XML, JSON)
- Bot defense using deception, biometrics, and AI for accurate detection
- Available as hardware appliance, virtual machine, SaaS, and in public clouds
Enterprise features include:
- AI-based zero-day threat prevention with minimal management overhead
- Security Fabric integration with FortiGate and FortiSandbox for extended threat defense
- Threat analytics and remediation playbooks for faster incident response
- Hardware acceleration with industry-leading throughput (up to 70 Gbps)
- Multi-model deployment for scaling across hybrid or multi-cloud environments
Imperva web application firewall is a security solution to protect web applications and APIs across on-premises, cloud, or hybrid environments. It blocks attacks like SQL injection, cross-site scripting (XSS), and other OWASP Top 10 threats with few false positives. It provides continuously updated rules, enabling organizations to deploy in blocking mode.
General features include:
- Protects applications and APIs in any deployment environment (cloud, hybrid, or on-premises)
- Out-of-the-box managed rules tested in production for immediate blocking mode deployment
- Near-zero false positives with high detection accuracy
- Automated policy creation and regular rule updates by Imperva Research Labs
- Machine learning for behavioral analysis and threat correlation
Enterprise features include:
- SSL lifecycle management including certificate automation, renewal, and observability
- Attack analytics to correlate multiple alerts into clear, actionable incident views
- Terraform provider for Infrastructure-as-Code (IaC) deployment and management
- Continuous compliance support for GDPR, PCI DSS, and other data protection standards
- Centralized multi-site management from a single dashboard
F5 BIG-IP Advanced WAF is a web application firewall to secure applications and APIs against advanced threats, including zero-day vulnerabilities, layer 7 denial-of-service attacks, credential theft, and malicious bots. It uses behavioral analytics, machine learning, and in-browser encryption to detect and block attacks that evade traditional signature-based defenses.
General features include:
- Protects against OWASP Top 10 threats, zero-day exploits, and L7 DoS attacks
- Behavioral analytics and machine learning for accurate threat detection
- Protection for APIs including REST, GraphQL, JSON, XML, and GWT
- In-browser application-layer encryption to prevent data theft from malware or browser-based attacks
- Bot mitigation and credential-stuffing prevention
Enterprise features include:
- Declarative, API-based configuration for seamless DevSecOps and “security as code” workflows
- Security policy management for microservices and distributed apps
- Integration with public cloud platforms (AWS, Azure, GCP) and private cloud or hypervisors
- Customizable threat intelligence feeds to adapt defenses to emerging campaigns
- Protection against targeted attack campaigns through behavioral DoS mitigation and analytics
Source: F5
Cloudflare WAF is a globally distributed web application firewall to detect and block threats in real time, including zero-day exploits, automated attacks, and credential theft. Cloudflare’s network handles over 100 million HTTP requests per second, using machine learning and global threat intelligence to deliver protection across environments.
General features include:
- Blocks OWASP Top 10 threats including SQL injection and cross-site scripting (XSS)
- Threat detection using global threat intelligence from the Cloudflare network
- Machine learning-based protection against emerging threats and zero-day attacks
- Fast, no-code deployment with simple onboarding and no training required
- Scans uploaded files for malware to protect applications from malicious content
Enterprise features include:
- Detects and blocks credential stuffing and account takeover attempts
- Rate limiting to prevent abuse and resource exhaustion
- Integrated with Cloudflare’s application security portfolio for unified protection
- Operates on a global edge network, reducing latency while enhancing security
- Managed rules with continuous updates for proactive zero-day mitigation
Conclusion
Web application firewalls are a critical layer of defense in securing enterprise applications against increasingly complex and automated threats. By inspecting traffic at the application level, WAFs help mitigate risks, enforce compliance, and maintain availability. As application architectures evolve, modern WAFs must adapt to protect APIs, integrate with development workflows, and scale across cloud and on-premises environments.