What Is A WAF? 2024 Guide to Web Application Firewalls

1. Network-based WAF

This is generally a hardware-based solution that is installed locally on the network infrastructure. It offers low latency and high performance, which is crucial for real-time applications. However, it is also expensive and requires physical maintenance. In most cases these devices are self-maintained and configured which requires internal resources and a certain level of knowledge. Network-based WAFs are typically used by large organizations that have the resources to manage and maintain the physical equipment.

2. Software-based WAF

This type of WAF is managed by a service provider that offers the WAF on a "security-as-a-service" basis. Software-based WAFs provide additional customization options and are typically less expensive than network-based WAFs. However, their filtering and monitoring processes may be slower, as they are run on top of a virtual machine. These WAFs can be deployed for different servers, offering a lot of flexibility.

3. Cloud-based WAF

Cloud-based WAFs offer an affordable and easy-to-implement option. They usually offer a turnkey installation that is as simple as a change in DNS to redirect traffic. Los WAF basados en la nube también tienen un costo inicial mínimo, ya que los usuarios pagan mensual o anualmente por la seguridad como servicio. They can offer a solution that is consistently updated to protect against the newest threats without any additional work or cost on the user's end. Some Cloud WAF vendors offer managed services that can remotely assist with configuring and managing the WAF. El inconveniente de un WAF basado en la nube es que los usuarios ceden la responsabilidad a un tercero. This means that some WAF features can be a "black box" for them.

Inline vs. Out of Path (OOP)

Lo ideal es que un WAF ofrezca la opción de implementarse en línea, donde la solución puede servir como "intermediario", o como un servicio fuera de ruta (OOP) basado en API. Una implementación OOP basada en API puede ofrecer varias ventajas únicas que le permiten ser optimizada para entornos multi-cloud. Permite que las peticiones de las aplicaciones vayan directamente del cliente al servidor de aplicaciones sin interrupción. Benefits include reduced latency, no traffic redirection and no need for SSL certificate sharing, increased uptime, and comprehensive protection across heterogeneous environments.

A network firewall operates primarily at the network and transport layers (layers 3 and 4 of the OSI model). Its primary function is to separate a secure zone from a less secure zone and control communications between the two. It acts as a barrier that prevents unauthorized access to the network as a whole. Network firewalls handle lower layers and are typically associated with protecting the network infrastructure. They monitor and control incoming and outgoing network traffic based on predetermined security rules.

A WAF provides protection at the application layer (layer 7 of the OSI model). A WAF protects web applications by monitoring and guarding Hypertext Transfer Protocol (HTTP) traffic. It sits between external users and web applications to analyze all HTTP communication. It then detects and blocks malicious requests before they reach users or web applications. As a result, WAFs secure business-critical web applications and web servers from zero-day threats and other application-layer attacks.

• WAF (Web Application Firewall): A WAF primarily secures web applications by filtering and monitoring HTTP/S traffic at the application layer (Layer 7 of the OSI model). It is specifically designed to detect and block threats targeting web applications, like the OWASP Top 10.
• IPS (Intrusion Prevention System): An IPS focuses on detecting and preventing attacks at the network level (typically Layers 3 and 4). It analyzes network traffic for signs of known vulnerabilities and exploits, such as buffer overflows, protocol violations, and brute force attacks. It lacks the deep application-layer protection that a WAF provides.

• NGFW (Next-Generation Firewall): An NGFW combines traditional firewall capabilities with advanced features like deep packet inspection, intrusion prevention (IPS), and application awareness. It protects both network and application traffic by filtering based on security policies and detecting advanced threats. NGFWs try to balance between IPS-like network protection and some WAF-like application-layer security, but they don’t offer the same level of protection, visibility, granularity or customization for web application threats that a dedicated WAF provides.

Dual Security Models

WAF should ideally combine both positive and negative security models. This combination allows the WAF to mitigate known web application attacks, such as access violations, attacks disguised behind Content Delivery Networks (CDNs), API manipulations and assaults, HTTP/S floods, brute force assaults, and others. Además, esta combinación también proporciona protección contra ataques y vulnerabilidades desconocidas, como los ataques de día cero.

Deep and Complete Coverage of the OWASP Top 10: A WAF should provide extensive security coverage that includes all the vulnerabilities listed in the OWASP Top 10. This ensures that the most critical security risks to web applications are well protected.

Protection Beyond the OWASP Top 10: In addition to covering the OWASP Top 10, a WAF should also provide protection against unknown and zero-day attacks. This means that the WAF should be capable of securing web applications from threats that are not yet known or have not been previously encountered.

API Discovery and Protection

A WAF should provide API discovery and protection that offers visibility, enforcement and mitigation of all forms of API abuse and manipulation, whether for on-premises or cloud-hosted environments. It should cover the OWASP Top 10 API Security Risks. As many of those risks are associated with the application business logic, it should be able to map the application API business logic and mitigate BLA in real-time.

Integration with Bot Management Solutions

A WAF should have the ability to integrate with bot management solutions to detect and mitigate sophisticated, human-like bots.

Real-Time Policy Optimization

A WAF should leverage behavioral-based, AI and machine-learning algorithms to create and optimize security policies in real-time. This capability ensures comprehensive protection while producing minimal to no false positives. It also provides automatic detection and protection of new applications as they are added to a network.

Core Features

The core features of a WAF should include the ability to filter network and application traffic based on geo-blocking, IP groups, blocklists, allowlists, whitelisting and blacklisting.

Built-In DDoS Protection

To counter application-layer DDoS attacks, a WAF should have built-in DDoS protection.

Client-side Protection: A WAF should also include client-side protection to secure end users from attacks embedded in the application supply chain. This extends the protection against supply-chain attacks via third-party APIs to offer protection against attacks that do not go through the server and are thus not detected by traditional WAFs. This capability is required to adhere to several compliance standards such as PCI DSS 4, NIS2, and DORA.

Data Leakage Prevention Mechanisms

To protect sensitive user data, such as personally identifiable information (PII), a WAF should have data leakage prevention mechanisms.

IP Fencing

IP fencing, also known as IP allowlisting or blocklisting, is a technique where a WAF restricts access to a web application based on the client's IP address. This method allows administrators to define a list of trusted IP addresses that are allowed to access the application, while blocking traffic from unknown, untrusted, or malicious IPs.

This can be particularly effective in preventing attacks from known malicious actors, such as those operating from IP ranges associated with botnets or cybercriminal groups. IP fencing is often used to protect internal systems by allowing access only from internal or VPN-secured IP addresses. While this method is useful for blocking large-scale attacks from specific regions or networks, it may not be sufficient for sophisticated attackers using techniques like IP spoofing or rotating through large pools of IP addresses.

Geo-Fencing and Geo-Blocking

Geo-fencing and geo-blocking are methods that limit access to a web application based on the geographical location of the user, which is determined by analyzing their IP address. Geo-fencing creates virtual boundaries, allowing or denying traffic from specific regions. For example, if an organization only serves customers in North America, they can block traffic from other continents, reducing their attack surface.

Geo-blocking, which is more aggressive, denies traffic from entire regions or countries known for a high frequency of cyber-attacks. However, these methods should be used with caution as attackers may use proxy servers or VPNs to mask their true location, bypassing geo-based restrictions.

Request and Response Inspection

Request and response inspection involves analyzing the data in both incoming requests and outgoing responses between the web application and the user. This method allows the WAF to monitor for malicious content or behavior embedded in HTTP/S requests, such as SQL injection attempts, cross-site scripting (XSS), Server-side Request Forgery (SSRF), or other forms of code injection.

The WAF inspects parameters, headers, cookies, and the body of the request to ensure they adhere to security policies and do not contain malicious payloads. Similarly, the WAF inspects responses to detect sensitive data leakage, such as unintentional exposure of personal information, authentication tokens, or server configuration details. By performing deep packet inspection on both ends of the communication, the WAF ensures that attacks are blocked before they can be executed, and sensitive information is protected from being exposed to attackers.

Security Rules

Security rules are a core WAF functionality, defining specific criteria that determine which traffic should be allowed or blocked. These rules can be based on various factors such as known attack patterns (e.g., SQL injection, XSS), anomalies in HTTP request headers, malformed requests, or even the presence of specific keywords or character sequences that are indicative of an attack.

Most WAFs come preloaded with rulesets designed to address common vulnerabilities and exploit techniques as identified by organizations like OWASP (e.g., OWASP Top 10 vulnerabilities). However, administrators can also create custom rules tailored to the unique needs of their application, such as blocking requests to sensitive endpoints or enforcing strict validation on user input fields. A WAF should continuously update its ruleset to account for new attack techniques, zero-day vulnerabilities.

Anomaly Scoring

Anomaly scoring is an advanced technique that assigns numerical scores to individual requests based on how closely they match malicious behavior patterns. Each suspicious activity or deviation from normal traffic-such as sending unusually large payloads, accessing unexpected resources, or attempting to exploit known vulnerabilities-adds to the anomaly score. When a request's cumulative score surpasses a predefined threshold, the WAF treats it as malicious and blocks it from reaching the application.

This method is particularly valuable in detecting sophisticated or zero-day attacks that do not match any known attack signatures but exhibit unusual patterns. Anomaly scoring allows the WAF to "learn" what typical, legitimate traffic looks like over time, improving its ability to detect outliers and potential threats without relying solely on static rules. This adaptive capability is crucial for defending against new and evolving threats that are not covered by predefined rule sets.

Inteligencia sobre amenazas

Threat intelligence is a proactive method used by WAFs to enhance security by leveraging real-time data on emerging threats from external sources. By integrating threat intelligence feeds, a WAF can automatically update its defenses based on the latest information about known malicious IP addresses, domains, botnets, and attack vectors. These intelligence feeds are continuously updated by security researchers, vendors, and global cybersecurity communities, providing insights into new vulnerabilities, zero-day exploits, and cyberattack trends.

For example, if a new vulnerability is discovered in widely used software, a threat intelligence feed can immediately inform the WAF, enabling it to block any attempts to exploit that vulnerability before a patch is even released. Additionally, threat intelligence can help identify large-scale, coordinated attacks, such as DDoS campaigns or botnet-driven attacks, and enable the WAF to take preventive action by blocking traffic from malicious sources.

Compliance Requirement: In many verticals today, having a WAF is not just a security best practice—it’s a compliance requirement. Regulatory standards such as PCI DSS and NIS2 mandate the use of a WAF to protect against web application attacks.

Agile Development Methodologies: While these methodologies allow for rapid development and deployment, they can also introduce new vulnerabilities into web applications if not properly managed. A WAF can provide the necessary security controls to mitigate these risks.

Shift to the Cloud: As more organizations move their operations to the cloud, they must also contend with the unique security challenges that this environment presents. A WAF can provide consistent security policies across on-premises and cloud environments.

Increased Use of Web-Based Software or SaaS Applications: These applications can be targeted by attackers due to their widespread use and internet-facing nature. A WAF can protect these applications by filtering, monitoring, and analyzing HTTP and HTTPS traffic.

Volume and Diversity of Attacks: With the increasing volume and diversity of web application attacks, it’s virtually impossible to protect applications without a WAF. A WAF protects web applications from a wide range of attacks such as cross-site forgery, server-side request forgery, file inclusion, and SQL injection, among others. It also safeguards applications and websites against the most critical security vulnerabilities (visit OWASP Top 10 to see the full list) including, but not limited to:

• Injection Attacks: This category includes both cross-site scripting (XSS) and SQL Injection attacks. In these types of code injection attacks, adversaries insert malicious scripts or SQL statements into a legitimate website or web application’s database query software. This can potentially allow the attacker to steal sensitive information, impersonate the user, or modify or delete information in the database.
• Security Misconfiguration: This category includes various types of attacks that exploit misconfigurations in web applications, including some forms of application-layer DDoS attacks.
• Vulnerable and Outdated Components: This category addresses risks associated with using components with known vulnerabilities, which can be exploited by attackers.