What is an Application-level Firewalls in information security?

An application firewall is a type of firewall that search, monitors and controls network, web and local system access and operations to and from an application or service. This type of firewall creates it possible to control and handle the operations of an application or service that is outside to the IT environment.

Application firewalls secure application communications in a same manner that network firewalls take network communications. Because they are familiar of the languages applications use to transmit data, they can deny or change invalid or suspicious activities protecting organizations against attacks.

An application firewall is generally used as an improvement to the standard firewall program by supporting firewall services up to the application layer. Many services performed by an application firewall contains controlling the execution of applications, data handling, blocking malicious code from being executed and more.

Proxy firewalls implement stateful and deep packet inspection to compute the context and content of data packets against a group of user-defined rules. It is based on the outcome, they allows or discard a packet. They secure the identity and location of the sensitive resources by avoiding a direct connection between internal systems and external networks.

An application gateway is an application program that runs on a firewall system among two networks. It is called a application proxy or application-level firewalls. When a client program makes a connection to a destination service, it connects to an application gateway, or proxy. The client then compromises with the proxy server to communicate with the destination service.

The proxy creates the connection with the destination behind the firewall and acts on the favor of the client, hiding and securing individual computers on the network behind the firewall. This makes two connections including one between the client and the proxy server and one between the proxy server and the destination.

Because connected, the proxy creates all packet-forwarding decisions. Because all communication is conducted through the proxy server, computers behind the firewall are secured. While this is treated a highly secure technique of firewall protection, application gateways require large memory and processor resources compared to other firewall technologies, including stateful inspection.

A WAF or web application firewall helps secure web applications by filtering and monitoring HTTP traffic between a web application and the Internet. It generally secure web applications from attacks including cross-site forgery, cross-site-scripting (XSS), file inclusion, and SQL injection, etc.

A WAF is a protocol layer 7 defense (in the OSI model), and is not designed to protect against some types of attacks. This approach of attack mitigation is generally part of a suite of tools which make a holistic defense against a range of attack vectors.