What Is a Web Application Firewall and Do You Need One?

In 2025, organizations depend on web applications for everything from customer engagement to internal systems. Web apps are now business-critical—but they are increasingly under attack. Unlike network-layer attacks, which focus on brute force or protocol-level flaws, application-layer attacks exploit business logic and user interactions. These attacks are often subtle, dangerous, and designed to slip past traditional defenses.

A Web Application Firewall (WAF) plays a vital role in application layer attack prevention. Positioned between the internet and your web infrastructure, a WAF analyzes HTTP and HTTPS traffic to detect and block malicious payloads before they can execute. The WAF inspects intent—scrutinizing user behavior in real time using web traffic inspection techniques.

What Is a Web Application Firewall?

A Web Application Firewall is a security solution that filters, monitors, and controls traffic to and from web applications. Operating at the application layer of the Open Systems Interconnection (OSI) model, it identifies threats that traditional firewalls often miss.

WAFs examine headers, cookies, body content, and parameters in incoming requests. Based on pre-defined rules or machine learning, they block malicious traffic such as SQL injection attacks, prevent cross-site scripting (XSS), rate-limit suspicious activity, and alert administrators to anomalies.

Many modern WAFs also ingest threat intelligence feeds to identify and block known attacker infrastructure.

Threats a WAF Can Mitigate

A properly configured WAF can help protect against:

• SQL Injection Protection: Attackers embed malicious code into applications. Hackers ran a series of attacks using the now notorious MOVEit SQL injection vulnerability in 2023.

• Cross-Site Scripting (XSS): Malicious scripts are injected into trusted web pages, enabling session hijacking.

• Remote Code Execution (RCE): Attackers run arbitrary code on target systems.

• Protocol Anomalies: WAFs detect malformed or irregular HTTP requests.

According to the Open Web Application Security Project (OWASP) some of these threats remain among the top risks in application security. OWASP is set to announce its top ten in late summer or fall of 2025.

Cloud WAF vs Appliance WAF

When deciding between a cloud WAF or an appliance WAF model, organizations must weigh scalability, control, and resource overhead.

• Cloud-based WAFs, such as AWS WAF, are managed by external providers. These are easy to deploy, scalable, and require minimal upkeep.

• On-premises WAFs offer control and customization but come with higher maintenance overhead.

• Host-based WAFs reside on the web server itself, offering developers fine-grained control.

Each option involves trade-offs in performance, visibility, and management complexity.

Does My Business Need a WAF?

Even teams with strong secure development lifecycles benefit from WAFs that can catch implementation oversights. Your organization should consider a WAF, especially if it:

• Operates public-facing web applications or Application Programming Interfaces (APIs)

• Handles regulated or sensitive data such as healthcare records or financial information

• Develops custom software prone to logic flaws

• Falls under compliance mandates like the Health Insurance Portability and Accountability Act (HIPAA), Payment Card Industry Data Security Standard (PCI DSS), or the General Data Protection Regulation (GDPR)

• Operates in a high-risk industry or experiences frequent attack attempts

WAFs Provide More Than Just Protection

Beyond blocking attacks, a Web Application Firewall enhances security operations by:

• Generating logs for compliance and audit readiness

• Increasing visibility into attack patterns and trends

• Automating responses to known malicious activity

• Blocking bot traffic involved in credential stuffing or content scraping

These WAF security features can help reduce the burden on security operations teams and improve response coordination across DevOps and compliance stakeholders.

WAF Limitations You Should Understand

A WAF is not a silver bullet. WAFs do not replace secure coding, vulnerability management, or penetration testing. Its effectiveness can be limited by:

• False positives, which block legitimate user actions

• False negatives, which allow novel or highly targeted attacks to bypass detection

• Maintenance demands, including rule tuning and regular updates

WAFs and Supply Chain Security

Threat actors are no longer just targeting organizations directly—they are increasingly attacking through the supply chain. For instance, hackers can use a vulnerable third-party SaaS application as a launching pad from which to access customer networks.

Over one-third of breaches now originate from third parties, according to SecurityScorecard’s 2025 Global Third-Party Breach Report. SecurityScorecard’s Supply Chain Detection and Response (SCDR) platform complements WAF defenses by identifying high-risk software fingerprints, exposed ports, and unpatched services across your vendor ecosystem.

Measuring Vendor WAF Hygiene Using Security Ratings

WAF deployment isn’t only an internal concern. Vendors and suppliers also present risk if their web infrastructure is insecure. SecurityScorecard provides visibility into indicators that may reflect poor WAF deployment or missing protections—such as exposed application-layer services and more:

• Exposed web applications across over 12 million rated entities

• Botnet-linked communications

• Vendor behaviors that signal low patching cadence

Pairing internal telemetry with external ratings can enable better decisions during vendor onboarding and continuous monitoring.

Executive Summary

Web Application Firewalls have evolved into essential tools for protecting digital infrastructure, particularly as applications are increasingly central to business operations. WAFs can provide critical safeguards against common attacks, improve visibility, and support regulatory compliance—but only if integrated properly and maintained continuously.

WAFs are especially vital for organizations operating in high-risk industries or managing complex vendor ecosystems.

SecurityScorecard helps organizations advance their application security strategies through continuous monitoring and actionable risk intelligence. Platforms like SCDR complement WAFs by revealing external application-layer exposures before attackers can exploit them.

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