What is a Web Application Firewall (WAF)?

What is a Web Application Firewall (WAF)

A web application firewall (WAF) helps safeguard web applications against incoming attacks by monitoring, filtering and blocking traffic according to security policies. A WAF may be deployed as software or hardware solutions with customizable policies tailored specifically for each business’s security requirements.

As part of an application security program, it’s crucial that firewall rules are configured appropriately so as to avoid false positives or negatives and ensure the WAF remains up-to-date in order to address ever-evolving threats.

What is a Web Application Firewall WAF?

WAFs (Web Application Firewalls) are designed to shield web applications from security threats like zero-day attacks, botnets and malware. A WAF intercepts HTTP (Hypertext Transfer Protocol) traffic using rules or policies in order to filter out bad traffic; identify patterns of behavior which indicate attacks; block requests that do not comply with those policies; identify patterns that indicate an attack and provide visitors with an Opportunity Test to Tell Computers and Humans Apart (CAPTCHA) test which only human visitors can pass; malicious bots cannot.

WAFs can be deployed as software, hardware or as a waf-as-a-service and feature custom security policies tailored specifically for each web application’s needs. They must also remain up-to-date to counter hackers who continually craft attacks targeting known vulnerabilities. WAFs can also work in concert with other security tools, such as an intrusion detection system (IDS), intrusion prevention system (IPS), or next-generation firewalls to provide a multilayered defense against threats that slip past general network and application layer protection measures. The best WAFs offer both positive and negative security models by using whitelisting – which only allows authorized traffic into a web application – and blacklisting, which uses up-to-date signatures against known vulnerabilities to block specific content – to create the optimal solution.

How does a web application firewall WAF work?

A WAF sits between your web applications and networks to intercept, inspect and block malicious traffic before it can reach them. It uses multiple filters to identify web exploits like cross-site request forgery (CSRF), buffer overflow attacks and command and control communications used during DDoS attacks. WAFs typically employ either whitelist/allowlist or blacklist security models depending on predetermined rules that have been approved beforehand.

WAFs analyze all components of HTTP conversations, from retrieving information from servers to sending data changes directly. They use signature-based detection to recognize known attacks as well as anomaly-based detection to detect behavior that doesn’t match established patterns of attacks.

WAFs combine techniques that can effectively detect new and emerging threats to protect against new cyber attacks as they emerge, yet cyber attackers continue to adapt. Therefore, WAFs require constant monitoring and updates so as to identify emerging vulnerabilities, both via automated analysis as well as manual inspection.

Key Benefits of a WAF

WAFs are essential components of any web-based business that relies on web applications. They help protect data leaks and unauthorized access as well as meet compliance standards like PCI DSS compliance. Furthermore, WAFs help protect APIs as well as improve server performance by offloading SSL/TLS decryption duties from them.

WAFs use rules, OWASP detection patterns and threat intelligence to quickly recognize attack behavior and block it before it affects web applications. Unlike traditional firewalls, WAFs can detect complex threats operating over web protocols as well as signature-based detection for traffic that matches known attack patterns like SQL injection, cross-site scripting (XSS) or directory traversal – unlike their traditional counterparts which rely on rules alone for detection and blocking attacks.

Outbound protection can protect data from being leaked out into the wild and meeting attackers’ goals, such as leaking confidential information or credentials. Most WAFs offer some level of customization so security policies can be applied selectively without blocking legitimate requests; some even come equipped with features like IP rate limiting, CAPTCHA verification, device fingerprinting and human interaction challenges to detect and block bad bots scraping your website for competitive information.

Web Application Firewall WAF Best Practices

WAFs can be deployed either in-line, as a middleman between an application server and client, or out of path (OOP), via API-based solutions. With in-line deployment, they should ideally sit behind load balancing tiers to maximize performance, reliability and visibility.

A WAF should be capable of detecting web application threats and vulnerabilities instantly through rules-based security models, like a blacklist- or blocklist-based security model, which allow only traffic that complies with predetermined patterns or behaviors (similar to club bouncers rejecting guests who do not meet dress code restrictions).

A good WAF should also be capable of detecting and mitigating threats through various means, including rate limiting which prevents attacks by restricting how many requests from any one IP address can come through within a specified time. Some WAFs also feature bot detection/mitigation features, SSL/TLS offloading to reduce server strain, integration capabilities that work alongside other security tools for enhanced protection, etc.

1. Put WAF in Front of Every API

A WAF deployed in front of an API can detect and prevent common attacks like code injection, cross site scripting (XSS), application layer DDoS attacks, bot scraping attempts for competitive data and brute-forcing attempts.

An ideal solution will combine a WAF with other security mechanisms like API gateways and threat intelligence in order to protect against both external malicious actors as well as attackers within your environment. This approach ensures your APIs are as carefully protected as those who access them.

WAFs can be implemented either inline or transparently as a bridge, depending on your business needs, scalability requirements and technical resources. Network-based WAFs may be best for companies with limited budgets and/or resources while cloud-based WAFs provide public cloud benefits with customisable scalability that meets specific business needs. Both options can be tailored to your security requirements by setting rules.

2. Continuously Test WAF Changes

Most WAFs require significant tuning to provide adequate protection. To do this effectively, security teams must carefully balance the needs of their business with risk associated with blocking legitimate traffic while permitting malicious traffic through. Furthermore, regular evaluation and testing of their WAF is crucial in order to ensure it continues protecting applications against potential attacks.

WAFs differ from network firewalls in that they observe web application activity at its original host server, making evaluating and testing of its configuration and rules more time consuming and challenging. Security teams should utilize data from penetration testing tools in order to test any changes before they enter production.

As cybersecurity threats constantly evolve, the WAF must be actively maintained to detect emerging vulnerabilities and attack methods. This can be challenging with agile development teams pushing code into production multiple times each week; DevOps practices can ensure that developers work alongside operations personnel as well as security personnel to update the WAF on an expedient basis.

3. Make Security Part of the Code

Web applications and APIs are susceptible to security risks that threaten to disrupt operations or exhaust resources, including malicious bots. A WAF provides protection from such threats by intercepting bi-directional HTTP (Hypertext Transfer Protocol) traffic and analyzing it to detect suspicious activities and block them.

WAFs may operate using both positive and negative security models, with whitelisting application requests to permit known-good traffic through while blacklisting attack patterns to block attacks such as code injection, cross site scripting (XSS), Layer 7 DDoS assaults etc. Additionally, machine learning technologies create and optimize security policies in real-time with minimal false positives for new vulnerabilities or attacks that emerge.

WAFs can be deployed using software, hardware or the cloud – the type you select depends on your business needs and scalability requirements. Network WAFs are ideal for large enterprises with distributed applications requiring high performance; they can be placed close to field applications to reduce latency and scale more effectively than software-based WAFs which require libraries on an application server as well as consuming CPU and RAM resources.

Types of Web Application Firewalls

Web Application Firewalls (WAF) offer protection from cyber attacks targeting web applications and websites. WAFs identify, monitor, and filter data packets in order to fend off SQL injections, cross-site scripting attacks, etc.

WAFs also prevent DDoS attacks and help meet compliance standards such as GDPR, CCPA and HIPAA. Solutions may be host-based, network-based or cloud-native.

1. Network-based WAFs

Network-based WAFs sit in front of web applications to monitor and filter HTTP communication. By applying a set of rules to identify what parts of an HTTP conversation may be malicious and which ones harmless, this allows for a high degree of customization while also limiting false positives.

WAFs typically operate at OSI model Layer 7 –the application layer– as opposed to network firewalls which work at layer 4 to protect endpoints such as servers and devices. Therefore, network-based WAFs do not serve as replacements for an NGFW and will not stop web attacks in all cases.

A network-based WAF solution should offer a customizable dashboard and granular granularity to customize security policies to the business, real-time alerts, and reporting to enable teams to respond more rapidly to threats and vulnerabilities. Furthermore, it should detect DDoS attacks and forward traffic directly to an anti-DDoS platform for mitigation purposes.

2. Cloud-based WAFs

Network-based WAFs are deployed at the network perimeter to safeguard web applications by inspecting traffic before it reaches their applications. Multiple web apps can be protected simultaneously with one WAF providing a central point for management, monitoring, and oversight. They may be implemented as either inline reverse proxy solutions or API-based out-of-path solutions.

As well as detecting and blocking attacks, they can also detect malware by monitoring incoming traffic for suspicious requests such as GET, POST or DELETE requests which could be used to steal data, create new content or attempt brute force logins. They also help mitigate denial of service (DoS) attacks by restricting how much traffic reaches an application while blocking IP addresses of attackers who attempt brute force logins.

Cloud-based WAFs typically come as software solutions or appliances and can be configured via a web interface, making deployment easy in virtual machines (VM), virtual private clouds (VPC), or private clouds with pay-as-you-go pricing models.

3. Hardware-based WAFs

WAFs operate at the application layer (OSI model Layer 7), offering protection from web app attacks such as SQL injection, cross-site scripting and cookie manipulation. They can also protect against DDoS attacks while speeding up website performance through intercepting and filtering requests.

Anti-DDoS solutions come in the form of hardware appliances, software plugins or cloud services that analyze HTTP conversations to reduce or eliminate malicious traffic and protect against security threats such as DDoS attacks, cross-site scripting attacks and e-commerce fraud. They can be placed either at the network edge or within a company data center for installation.

Network-based WAFs can be configured to include pre-loaded security rules that detect common attack patterns and be tailored specifically for a company’s unique business logic. In conjunction with an IPS (intrusion prevention system), they may also help stop attacks that bypass their firewall. Host-based solutions offer full integration into an application software but typically consume more server resources, cost more, and require professional expertise for installation and ongoing management.

4. Behavior-based WAFs

Web application firewalls are security tools designed to monitor incoming traffic to websites and apps, identify any malicious patterns and block attacks. Web application firewalls offer protection from the most frequent cyberattacks such as cross-site scripting (XSS), SQL injection and DDoS attacks as well as sensitive data theft as well as comply with industry standards like PCI DSS or HIPAA.

WAFs can operate either transparent bridge or reverse proxy mode. The former involves binding ports and addresses to web applications so users are unaware that a proxy server exists – an approach that makes setup much simpler but does not provide much in terms of isolation from network apps or users.

Reverse proxy mode adds another level of complexity, but can offer more control when configuring a WAF. This allows it to be more selective about what it blocks and help prevent unwanted blocking of legitimate traffic.

Final Thoughts

A WAF acts as a buffer between your application server and the Internet, filtering incoming HTTP conversations for malicious activity and protecting web applications against attacks which exploit vulnerabilities or flaws in them.

The best cloud WAFs provide businesses with additional features that help protect their data, applications and customers from cyberattacks. For instance, they may include bot management that detects and blocks suspicious or harmful bot traffic while still permitting human visitors. Geofencing limits access from specific geographic regions while CAPTCHA tests or user interaction challenges verify if someone is human before granting access.

A strong WAF can identify and report suspicious activity to analysts, providing valuable insight into potential security concerns.

Furthermore, it can be configured to operate in prevention mode to block malicious traffic before it ever reaches your application servers – significantly decreasing time and resources spent by teams on detection, reporting, and responding to common threats.

Sam is an experienced information security specialist who works with enterprises to mature and improve their enterprise security programs. Previously, he worked as a security news reporter.