Rating:

Was it a car or a cat I saw?
file: esab64

Notice that filename is base64 but backwardish. Read file backwards and decode as base64 using tac: tac -r -s 'x\|[^x]' esab64. This produces the flag but backwards so reverse again: tac -r -s 'x\|[^x]' esab64 | base64 -d | tac -r -s 'x\|[^x]' and get the flag

Flag: flag{fb5211b498afe87b1bd0db601117e16e}

Original writeup (https://thomaspreece.com/2021/03/15/nathamcon-ctf-2021/#5-esab64).