You could attack the dhcp server, like a dhcp starvation attack..
In case you have Cisco, you could attack the CDP..
You could attack the wifi network, especially those using WEP..
These are just some examples of attacks in case you are already inside the network..
ARP poisining and etc.. Rogue DHCP server, the list goes on...

In case you are from outside the network, there is a block all rule in WAN.
This block rule means that the firewall won't be accepting anything from outside.
In the other hand, you may have a port forward in which your server could be vulnerable, and not pfsense.

Also, as pfsense is a stateful firewall, it will allow the clients to go to the internet, and allow the packets to return automatically.
Based on that there is a possibility that you have a host that has a malware, botnet, or this host has a CPU vulnerability (MDS, TAA, Spectre/Meltdown) and thus is vulnerable to code execution, which, according to Arch linux security wiki, this host could be remotely exploited just by accessing a website running JAVA..

@nollipfsense thank you so much. But which are some examples of attacks ?

A properly configured firewall with IDS/IPS as well as pfBlockerNG mitigates attacks.

practicing to attack on pfsense using Kali Linux

If you're not confident of pfSense firewall, use others. BTW, there is no common attacks.