4min. read

What Is a Web Application Firewall (WAF)?

Protecting web applications and APIs is now a critical component for application security engineers, security architects, and information security professionals. This article will take a deep dive into web application firewalls, also known as WAFs. We’ll explore what they are, how they work, and how you can configure a WAF solution to better protect your applications and APIs.

Once we’ve covered how you can use a WAF solution to protect your applications against vulnerabilities, we’ll look into how you can use this technology to protect your applications moving forward and investigate web application and API security (WAAS). Let’s get started.

What Is a Web Application Firewall?

Web application firewalls were created and became popular toward the latter part of the 1990s as web applications grew in popularity and became the targets of cyberattackers. Early versions of WAFs protected applications against the submission of illegal characters, but they have since evolved to protect against many malicious threats and vulnerabilities that web applications face. The WAF sits between the application and the client, filtering the HTTP traffic to and from the web service and protecting against attacks such as XSS, or cross-site scripting, SQL injection and file inclusion. 

Understanding the Threat Landscape

Before we talk about the critical components of an effective web application firewall, let’s consider the different types of threats against your web application. We’ve already mentioned XSS, SQL injection and file inclusion. The objective of the original application firewalls was to protect against these types of attacks, but the battlefield has changed and continues to evolve. Denial of service or DoS/DDoS attacks are becoming more frequent as on-demand cloud computing and vulnerable IoT devices increase in popularity.

The most recent OWASP Top Ten list now includes more risks associated with access control and configuration than ever before. Broken access control and cryptographic failures occupied the top two spots on the list in 2021. Related problems like security misconfiguration and outdated components have also increased in prominence. Last but by no means least, in addition to protecting our services from attack, we also need to prevent personal and confidential data from being accidentally leaked from the web servers.

Critical Functions of an Effective Web Application Firewall

We can divide the function of the WAF into two distinct parts, specifically protecting inbound and outbound traffic. The inbound protection functionality of the WAF is responsible for inspecting all application traffic from the outside world. As part of protecting the application from inbound traffic, the WAF needs to identify dangerous activity patterns and suspicious payloads and vulnerabilities. Because hackers are persistent and innovative, the nature of these attacks is continually evolving. The firewall needs to be adaptive and use proactive measures to prevent these sophisticated attacks while simultaneously ensuring that it quickly filters legitimate requests to the application for processing.

Outbound protection is all about preventing your data and your customers’ data from leaking into the real world. As countries worldwide enact stricter legislation to support consumer privacy and the expectation that companies store and manage personal data securely, each new day seems to bring stories of data breaches and exposure of that same information. The WAF is an integral part of your security offense, ensuring that the application handles legitimate requests appropriately, while preventing personal and confidential data from leaking either accidentally or through malicious means.

Future of Web App and API Security (WAAS)

Modern web applications built on cloud native architectures are more complex than ever. Agile development processes, continuous integration and deployment, and environments that are constantly changing create new challenges for the traditional WAF. The next generation of web application and API protection is web app and API security (WAAS).

WAAS includes traditional WAF features like automatic discovery of web applications. It also goes a step further to discover all API endpoints within your environment. This approach simplifies configuring security rules to protect your web applications and APIs or update existing applications within your environment. By automatically detecting and protecting your web-facing application and APIs, you also reduce the risk that an application might be misconfigured or deployed without any manner of protection.

An effective WAAS solution will accept API specifications from various formats such as Swagger and OpenAPI and use these definitions to screen income requests to determine their conformity with the specification. Some endpoints may require less protection and greater access, while those handling sensitive data may require the highest level of protection and scrutiny. In addition, a WAAS solution includes DoS protection out of the box. 

Some additional features that you should consider when selecting a web application security solution is the ability to screen requests based on place of origin. You also want the ability to customize the level of the defensive measures applied for each application or API with custom rules. You may also want to set the level of alerting and error reporting from each application based on a combination of severity and potential risk.

Securing Your Apps for the Future

The future of cloud computing is both exciting and challenging to predict, but one thing is for sure: cloud native applications will continue to grow in both importance and complexity, and cloud native apps require constant protection from malicious vulnerabilities. Security products need to have the ability to evolve and adapt as quickly as the dynamic threats against which they are responsible for defending.

Information security professionals – DevOps engineers, security architects, and application security teams – have to collaborate and draw on the experience of others to build a comprehensive security strategy. Seek out partnerships with well-established security providers who have experience protecting the modern enterprise. 


Learn more about Palo Alto Networks Web Application and API Security (WAAS) solution, or get a free trial of Prisma Cloud.

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