What is a Web Application Firewall (WAF)?

A web application firewall, often abbreviated as a WAF, protects web apps by monitoring and filtering HTTP traffic between the Web and a web app. It typically protects online applications from file inclusion, cross-site forgery, cross-site scripting (XSS), and SQL injection, among other things. In the OSI model, WAF is a layer seven defense that is not intended to guard against all forms of threats. This form of attack prevention is typically part of a package of tools that, when combined, create a comprehensive defense against a variety of attack vectors.

When a WAF is deployed before a web application, it creates a barrier between the Web and the web app. A proxy server, on the other hand, protects the identity of a client machine by acting as a bridge, a WAF is a form of reverse proxy that protects the server from exposure by requiring users to go through the WAF before accessing the server.

A WAF runs according to a set of regulations, sometimes referred to as policies. These policies try to guard against application vulnerabilities by screening out harmful traffic. The utility of a WAF is partly from the ease and speed with which policy modifications may be deployed, allowing for speedier reaction to various attack vectors; for example, rate restriction can be swiftly imposed during a DDoS attack by modifying WAF policies.

What is the difference between blocklist and allowlist WAFs?

A blocklist-based (negative security paradigm) WAF defends against known threats. Consider a blocklist WAF to be a club bouncer who is told to refuse admission to guests who do not adhere to the dress code. An allowlist-based (positive security paradigm) WAF, on the other hand, only allows pre-approved traffic. That is analogous to the bouncer at a private party; he only accepts those whose names are on the list. Both allowlists and blocklists have advantages and disadvantages that is the reason many WAFs provide a hybrid security strategy that incorporates both.

What are network-based, host-based, and cloud-based WAFs?

A WAF's implementation is done in one of three methods, each with a set of advantages and disadvantages:

  • In most cases, a network-based WAF is hardware-based. They decrease latency because of their local installation, but network-based WAFs are the costliest solution and necessitate the maintenance and storage of physical hardware.
  • A host-based WAF can be entirely incorporated into the software of an application. This approach is cheaper and more customizable than a network-based WAF. The disadvantages of a host-based WAF are the complexity of the deployment, the use of local server resources, and the cost of maintenance. These components usually necessitate engineering work and can be pricey.
  • Cloud-based WAFs are a low-cost, easy-to-implement solution; they often provide a complete installation comparable in simplicity to a DNS update to reroute traffic. Cloud-based WAFs also offer a low upfront cost that is because consumers pay for security solutions on a monthly or annual basis. Cloud-based WAFs may provide a solution that has constant updates with the sole purpose of defending against the most recent attacks with no additional labor or expense on the user's part. The cloud-based WAF's disadvantage is that customers take over the responsibility to a third party, hence some WAF functions may be ineffective.


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