Analysis
The problem provides us with a .pcap file for analysis. It expects us to find a flag hidden in it.
Solution
The flag is not directly accessible in the .pcap. The only thing available is a trace of echo requests from one host to the server. The only difference between each one of the requests is a single bit at the end of the data section.
If we compile all of these bits from the packets in order, we get the following message:
FEE2FEE2FFEF22FFFF2EEE2FEFF2EFEE2FFEEFE2FFF2FFFF2F2F2F2F2E2FFEEFE2EFEE2EEE2FFE2FFEEFE2EFEF2FE2EF2FFEEFE2FFEF2FF2EF2EFF2FFEEFE2EE2F2FFEEFE2FFEEFF2FFEEFF2FFEEFF2FFEEFF2FFEEFF2FFEEFF2FFEEFF2FFEEFF2FFEEFF2FFEEFF2
The sequence is too well-behaved not to mean something. A little bit of trial and error leads us to the conclusion that the character 2 is a separator, and that the message is encoded in morse, where the character F represents dots (.) and the character E represents dashes (_). The decoded message is then presented:
WWFHOLY_SHEEEET_YOU_CAN_FIND_ME_??????????
By formatting this according to the flag format given in the problem description ("Flag is case insensitive, but follow the format wwf{fl46_f0rm47} "), we have:
wwf{HOLY_SHEEEET_YOU_CAN_FIND_ME_??????????}