Learn in the textbookFundamentals of Access Control and Network Defense Devices
DefinitionA WAF (Web Application Firewall) inspects the content of requests reaching a web application and stops attacks that exploit its weaknesses.
ExplanationAttacks that slip malicious commands into an input field arrive by the same route as normal traffic, so addresses and port numbers alone can hardly tell them apart. A WAF compares the content of each request with known attack patterns and keeps such attacks out. It is used on websites that accept user input, such as sign-up and search forms.
AnalogyLike an inspector who takes parcels that have already passed the gate and opens each box to check what is inside, not just the address.
Memory hookIt has Firewall in its name, but it reads what a request says, not where it is going. The W at the front stands for the Web, the thing it guards.