Avoiding 0.0.0.0/0 In Your Firewall When Using A WAF

The usage of 0.0.0.0/0 is well-known in firewalls and includes every IP address. If we allow network connections on a certain port, which should never use the 0.0.0.0/0 address range. In this article I will explain why we should try and avoid 0.0.0.0/0 on the firewall of your Web server when using a WAF.

The WAF

One of my most admired companies is Cloudflare. I like them as they are genuinely passionate about cryptography. But, their best service is WAF (Web Application Firewall) and which allows for the filtering and caching of Web content.

Basically, the WAF sits in-between the user (Alice) and Web servers (Bob). When Alice wants to access Bob’s server, she must go through the WAF. Two of the main functions of the WAF are then to provide Alice with content that Cloudflare has cached and for the WAF to filter incoming requests (and drop them, if required). We can also add “Are you a human?” tests.

With this WAF, there are then policies which Bob implements to stop Alice from doing bad things on his server. This can apply from Layer 3 and above in the network stack. This allows us to filter for anything in…