What Is a Web Application Firewall (WAF)?
A web application firewall (WAF) is a security tool that monitors and controls HTTP and HTTPS traffic between a web application and the internet. Unlike traditional firewalls that focus on traffic at the network level, WAFs operate at the application layer, scrutinizing requests and responses. This enables them to prevent vulnerabilities from being exploited at the application level.
WAFs use a set of predefined, customizable rules to filter out malicious access attempts. They serve as a critical line of defense against numerous web-based threats by blocking, filtering, and monitoring traffic. Their primary goal is to mitigate the risk of data breaches by preventing unauthorized data exposure.
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Web application firewalls can offer a range of capabilities, but their primary functions include the following.
1. Monitoring and Analyzing HTTP/HTTPS Traffic
WAFs continuously monitor HTTP and HTTPS requests to web applications, analyzing them for malicious activity. By examining incoming data, they can quickly detect anomalies that suggest an attack, such as SQL injection attempts or cross-site scripting efforts. This real-time inspection allows for prompt responses to potential threats.
The analysis process involves evaluating the syntax and semantics of requests. WAFs inspect headers, cookies, and other elements to ensure they adhere to established security policies. These measures help identify and block suspected malicious traffic before it can cause harm.
2. Blocking Malicious Requests Based on Predefined Rules
WAFs can block malicious requests through predefined rules. These rules are regularly updated to adapt to emerging threats, and can be customized to match an organization’s specific applications and business rules. They use pattern matching to identify and stop requests that resemble known attack vectors, such as malicious payloads in SQL queries or script tags in input fields.
By leveraging these rules, WAFs can distinguish between legitimate user requests and potential attacks. The blocking mechanism operates without affecting the user experience, ensuring that only harmful requests are filtered out.
3. Filtering, Inspecting, and Sanitizing Inputs to Prevent Attacks
WAFs filter and inspect inputs to web applications, ensuring that they do not pose a threat. They sanitize inputs to remove unwanted characters or patterns that may be used in attacks, such as SQL injection or cross-site scripting. This process helps in maintaining the application’s security posture by neutralizing malicious inputs before they can execute.
The sanitization process involves parsing inputs for threats and enforcing rules that prevent harmful data from reaching underlying databases or systems.
Here are some of the additional features and deployment options that WAF solutions may offer.
4. Negative vs. Positive Security Rules
Negative and positive security models are two approaches WAFs use to define and enforce security rules.
Negative security rules focus on identifying and blocking known threats. These rules match patterns of malicious behavior, such as payloads, signatures, or request anomalies. For example, they might block requests containing known SQL injection patterns or script tags. While effective against known attack vectors, negative rules require constant updates to keep up with evolving threats.
Positive security rules define what is explicitly allowed and block everything else. This approach is stricter, ensuring that only legitimate traffic, conforming to predefined criteria, reaches the application. For example, if an input field is only supposed to accept numeric values, a positive rule would block any non-numeric input. While highly secure, this model requires detailed knowledge of application behavior and can be challenging to implement and maintain in dynamic environments.
A well-configured WAF often combines both models to strike a balance between broad threat coverage and strict access control.
5. Inline vs. Out of Path (OOP)
WAFs can be deployed in inline or out-of-path (OOP) configurations.
In an inline deployment, the WAF is placed directly in the traffic path between users and the application. This allows it to inspect and block requests in real time. Inline WAFs offer immediate protection but can introduce latency and become a single point of failure if not properly managed.
In an out-of-path deployment, the WAF operates alongside the traffic flow, receiving mirrored traffic for analysis. Instead of blocking malicious requests directly, it alerts the application or network administrators. This approach minimizes latency and avoids disrupting legitimate traffic, but it requires additional mechanisms to act on detected threats.
6. Behavioral Detection
Behavioral detection in WAFs leverages application learning to build a detailed profile of an application’s normal behavior. This involves analyzing parameters such as HTTP methods, form field values, cookies, and other user interactions to create a baseline for what constitutes typical application usage. By comparing incoming traffic to this baseline, a behavior-based WAF can detect and respond to anomalies that may signal an attack.
For example, if an input field typically accepts numeric values within a defined range, and a user attempts to input text or values outside that range, the WAF can flag this as suspicious. Over time, as the WAF gathers more data, its profile becomes more accurate, reducing the chances of false positives.
7. AI-Driven Detection
Machine learning-powered WAFs analyze vast amounts of traffic data to classify behavior as either legitimate or malicious. They use probabilistic models to assess the likelihood of a security threat, which helps in reducing false positives compared to traditional rule-based or behavior-based approaches. Over time, these systems improve in accuracy, requiring minimal human intervention.
Deep learning, a subset of machine learning, takes this further by processing data in new ways. For example, one approach is to transform HTTP request packets into image-like formats for analysis. Convolutional neural networks (CNNs) can analyze these images to detect patterns indicative of web attacks. This allows for the detection of threats that may bypass conventional systems.
Web application firewalls are effective against almost all application-layer threats, including OWASP Top 10 for web applications. Here are some of the more common threats that are addressed by WAF solutions.
Injection Attacks
WAFs offer protection against injection attacks, which involve injecting malicious code into an application through input fields or URL parameters. These attacks exploit vulnerabilities to execute unauthorized commands. By inspecting inputs for patterns commonly associated with injections, such as SQL commands, WAFs block these attempts before they reach the application database.
Injection attacks are a prevalent risk due to their potential impact, including data theft and alteration. WAFs utilize multiple detection techniques, including signature-based and behavioral analysis, to identify and mitigate such threats. They act as gatekeepers, preventing unauthorized data manipulation.
Cross-Site Scripting (XSS)
Cross-site scripting (XSS) attacks target vulnerabilities in web applications to execute malicious scripts in a user's browser. WAFs help protect against XSS by analyzing and filtering out suspicious script tags and data input patterns that may lead to execution in a user's context.
WAFs deploy strategies like input sanitization, encoding, and content security policy enforcement to thwart XSS attempts. By intercepting these malicious scripts, WAFs ensure that only safe content is delivered to users.
Cross-Site Request Forgery (CSRF)
Cross-site request forgery (CSRF) involves tricking a user into performing unwanted actions on a web application in which they are authenticated. WAFs combat CSRF by validating requests to ensure they are legitimately initiated by users. Techniques such as token validation and referer header checks are implemented to determine request authenticity.
By verifying requests with unique tokens, WAFs prevent attackers from executing unauthorized actions in a user's context. This validation ensures that interactions with web applications are securely authenticated.
File Inclusion Attacks
File inclusion attacks occur when a web application improperly handles file paths, allowing attackers to include unauthorized files. WAFs prevent these attacks by analyzing file paths and blocking requests that attempt to access sensitive or unauthorized files.
By monitoring request paths and inspecting input fields associated with file operations, WAFs can intercept attempts to access restricted directories. This prevents the execution of malicious code included in unauthorized files.
Distributed Denial of Service (DDoS)
WAFs play a role in mitigating distributed denial of service (DDoS) attacks, which aim to overwhelm a web application with excessive traffic. While not a substitute for dedicated DDoS protection systems, WAFs improve defenses by identifying and filtering abnormal traffic patterns indicative of such attacks.
Many DDoS attacks target application resources, making them unavailable to legitimate users. By differentiating between malicious and normal traffic, WAFs can throttle requests when unusual spikes are detected.
Server-Side Request Forgery (SSRF)
Server-side request forgery (SSRF) attacks exploit a server's capability to send HTTP requests, tricking it into accessing internal or unauthorized resources. Attackers may leverage SSRF to access sensitive data, escalate privileges, or pivot within a network.
WAFs mitigate SSRF by analyzing outgoing requests generated by the server. They enforce rules to validate the destination of these requests, preventing unauthorized access to internal endpoints or third-party services. WAFs also block requests containing suspicious payloads, such as malformed URLs or unexpected headers, that signal potential SSRF attempts.
Tips from the Expert:
In my experience, here are tips that can help you better secure and optimize your web application firewall (WAF) deployments:
1. Integrate WAF with SIEM tools for enhanced visibility: By integrating the WAF with a Security Information and Event Management (SIEM) solution, organizations can centralize and correlate logs from multiple sources, enabling advanced threat detection and streamlined incident response.
2. Use a layered defense strategy with WAFs: Combine WAF capabilities with endpoint detection and network firewalls. This layered approach ensures comprehensive protection against both application-layer and deeper systemic threats.
3. Implement rate limiting to combat abuse: Configure rate limiting in the WAF to control excessive requests from individual IPs or sessions, preventing API abuse, brute force attacks, or resource exhaustion while ensuring legitimate users are unaffected.
4. Utilize custom rules for niche threats: Default rules are useful but insufficient for highly customized applications. Develop custom WAF rules tailored to the application's unique architecture and known vulnerabilities to provide an additional layer of defense.
5. Enable and optimize TLS inspection: Modern threats often hide within encrypted traffic. Configure the WAF to inspect TLS traffic without impacting performance by using hardware accelerators or optimized cloud-based solutions.
WAFs vs. Traditional Firewalls
Traditional firewalls filter traffic based on IP addresses, port numbers, and protocols, focusing primarily on network-level threats. WAFs concentrate on application-layer protection, scrutinizing the content of data packets to guard against web vulnerabilities like SQL injections and XSS attacks. This focus makes WAFs more suitable for protecting web applications.
By targeting different layers, WAFs and traditional firewalls complement each other, providing a more comprehensive security posture. While traditional firewalls protect the network perimeter, WAFs address the nuanced threats targeting application logic and user data.
WAFs vs. Next-Generation Firewalls
Next-generation firewalls (NGFWs) extend the capabilities of traditional firewalls by incorporating features like deep packet inspection and intrusion prevention. While NGFWs focus on broader threat landscapes, WAFs specialize in detailed application-level protection. They scrutinize HTTP/HTTPS traffic with more granularity, tailoring defenses to web application threats.
The specialization of WAFs in application-layer security complements the broader functions of NGFWs. WAFs provide focused protection against intricate web attacks while NGFWs target network attacks and other advanced threats.
Learn more in our detailed guide to WAF vs NGWF
WAFs vs. Intrusion Prevention Systems
Intrusion prevention systems (IPS) detect and block malicious activities primarily at the network level by analyzing traffic patterns and signatures. WAFs apply their protection mechanisms directly to web applications by understanding application-specific traffic and logic structures. This makes WAFs particularly adept at defending against application-specific intrusions.
WAFs operate at a deeper, more granular level of application traffic, making them indispensable for securing web applications. IPS and WAFs can work in tandem to provide layered security.
Learn more in our detailed guide to WAF vs. IPS
WAF vs. WAAP
While web application firewalls (WAFs) focus on filtering, monitoring, and blocking web application attacks at the HTTP/HTTPS layer, web application and API protection (WAAP) extends this scope to cover API-specific threats. APIs are increasingly targeted due to their role in modern web applications, requiring security mechanisms beyond traditional WAF capabilities.
WAAP solutions integrate application-layer protections with API-specific features like schema validation, rate limiting, and OAuth enforcement. Unlike WAFs, WAAPs are tailored to protect microservices architectures and defend against API abuse. While a WAF may block malicious HTTP traffic, WAAP ensures API endpoints are secure against exploitation.
WAF vs. ASPM
Application security posture management (ASPM) tools focus on identifying and managing vulnerabilities in an application's development and deployment lifecycle. Unlike WAFs, which operate at runtime to block active threats, ASPM aims to improve security by identifying weaknesses during the build and testing phases.
ASPM tools provide insights into code vulnerabilities, misconfigurations, and insecure dependencies. They complement WAFs by reducing the number of exploitable flaws that attackers could target. Together, these tools create a holistic security approach, with ASPM focusing on prevention and WAFs providing active defense.
Organizations can improve the effectiveness of their WAF deployments by implementing the following best practices.
1. Choose the Right Deployment Model
Selecting the right deployment model for a WAF—whether on-premises, cloud-based, or hybrid—is essential for aligning with the needs and infrastructure of an organization. On-premises deployments provide control over hardware and software configurations, suitable for environments with stringent regulatory requirements and performance needs.
Cloud-based WAFs offer scalability and flexibility, minimizing the need for hardware investments and maintenance. Hybrid models combine benefits from both, allowing organizations to deploy the most appropriate features where needed. The choice affects performance, manageability, and integration capabilities.
2. Start with Default Rules
Implementing default rules provided by WAF vendors helps organizations kickstart their defense strategies. These pre-configured rules address common threats and vulnerabilities in web applications, such as SQL injections and XSS. They serve as a foundation for building a customized security policy.
Starting with default rules allows organizations to deploy WAFs quickly while gradually customizing rules based on application requirements and threat landscapes. This approach balances immediate protection needs with the flexibility to improve security measures over time.
3. Perform a Baseline Traffic Analysis
Conducting a baseline traffic analysis is crucial in understanding normal application behavior and identifying potential anomalies. Before deploying WAFs, analyzing traffic patterns helps organizations tailor WAF rules to suit their environment’s needs, reducing the risk of false positives and negatives.
By establishing a traffic baseline, organizations can differentiate between legitimate and suspicious activities. This analysis ensures that the WAF is configured to protect against genuine threats while maintaining application performance and user experience.
4. Enable Virtual Patching
Virtual patching is a strategy employed by WAFs to shield web applications from vulnerabilities without altering the application source code. It works by blocking exploit attempts on known vulnerabilities, giving development teams time to implement permanent fixes. This approach provides immediate protection against emerging threats.
WAFs implement virtual patches through rule updates that address vulnerability exploits. By enabling virtual patching, organizations can mitigate risks quickly and efficiently, maintaining application security while managing the development workload.
5. Regularly Update WAF Signatures
Regular updates to WAF signatures ensure that the protection capabilities of the security tool remain current with the latest threats. Attack vectors evolve rapidly, and outdated signatures can leave applications vulnerable. Regular updates improve the WAF's ability to detect and mitigate emerging threats.
Most WAF vendors proactively manage signatures by continuously monitoring threat feeds and issuing updates. WAF users should immediately apply these updates, and may need to manage conflicts with custom security rules. This process enables WAFs to adapt to new attack methodologies and protect against evolving vulnerabilities.
6. Leverage Bot Mitigation
Bot mitigation is essential in preventing automated attacks like credential stuffing and web scraping, which can harm web applications. WAFs equipped with bot mitigation features identify and control web robots by analyzing traffic patterns for signs of automation, distinguishing legitimate users from bots.
Implementing bot mitigation strategies ensures that only genuine traffic interacts with web applications, maintaining performance and service quality. By leveraging WAF capabilities for bot management, organizations can thwart malicious automated activities, protect sensitive data, and preserve application resources.
Radware offers several types of specialized WAF as well as malicious traffic detection and mitigation solutions based on user requirements:
Cloud WAF
Radware’s Cloud WAF service is part of our Cloud Application Protection Service which includes WAF, API protection, Bot management, Layer-7 DDoS protection and Client-Side Protection. The service analyzes web apps to identify potential threats, then automatically generates granular protection rules to mitigate those threats. It also offers device fingerprinting to help identify bot attacks, AI-powered API discovery and protection to prevent API abuse, full coverage of OWASP Top 10 vulnerabilities, and data leak prevention, which prevents the transmission of sensitive data. Radware Cloud WAF is NSS recommended, ICSE Labs certified, and PCI-DSS compliant.
Alteon Integrated WAF
Radware’s Alteon Integrated WAF ensures fast, reliable and secure delivery of mission-critical Web applications and APIs for corporate networks and in the cloud. Recommended by the NSS, certified by ICSA Labs, and PCI compliant, this WAF solution combines positive and negative security models to provide complete protection against web application attacks, access violations, attacks disguised behind CDNs, API manipulations, advanced HTTP attacks (such as slowloris and dynamic floods), brute force attacks on log-in pages and more.
Kubernetes WAF
Radware Kubernetes WAF is a comprehensive and scalable web application firewall designed for CI/CD environments orchestrated by Kubernetes. It provides robust data and application protection, integrating seamlessly with Kubernetes orchestration and common DevOps tools. The solution offers advanced automation, autoscaling, and elasticity, ensuring security for microservices architectures. It combines both negative (signature-based) and positive security models to protect against known and unknown threats, including zero-day attacks. Additionally, it provides detailed visibility and analytics for DevSecOps teams, reducing total cost of ownership with minimal false positives.
Bot Manager
Radware Bot Manager is a multiple award-winning bot management solution designed to protect web applications, mobile apps, and APIs from the latest AI-powered automated threats. Utilizing advanced techniques such as Radware’s patented Intent-based Deep Behavior Analysis (IDBA), semi-supervised machine learning, device fingerprinting, collective bot intelligence, and user behavior modeling, it ensures precise bot detection with minimal false positives. Bot Manager provides AI-based real-time detection and protection against threats such as ATO (account takeover), DDoS, ad and payment fraud, and web scraping. With a range of mitigation options (like Crypto Challenge), Bot Manager ensures seamless website browsing for legitimate users without relying on CAPTCHAs while effectively thwarting bot attacks. Its AI-powered correlation engine automatically analyzes threat behavior, shares data throughout security modules and blocks bad source IPs, providing complete visibility into each attack.