Synopsis

The synopsis says to "follow" the rabbit you'll understand why...

Step1: What to do ??

The web page shows us differents things...

But what to do next ? If we look closer, the get attribute "page" already has as parameter a base64 word, there is a kind of a same word in the web page. Let's try to replace it with the web page's word. Nice ! We have access to another web page

Step2: Let's follow the rabbit

Each web page conducts to another web page with the same kind of content. However, each one of them has a different first attribute. For example, the first page has: [513, '71'], the next one has [803, 'A5'] etc... At this point you need to guess that the first element of the attribute is a cell index and that the other one is the hex value of the cell. Let's retrieve them all in a big array.
Here is my script, I have just added a log file in case my idea was not the right one.

#!/usr/bin/env python3
import random
import string
import requests as rq

BASE="cE4g5bWZtYCuovEgYSO1"

def request_page(page):
    url = "http://167.71.246.232:8080/rabbit_hole.php?page="
    resp = rq.get(url+page)
    return resp

def parse_resp(resp):
    (num,new_page) =resp.split("\n");
    (index,value) = num[1:-1].split(",")
    return index,value,new_page[1:]

if __name__ == "__main__":
    TAB = [""] * 2000 #A big Array to have enough space
    page = BASE
    f = open("Log_pages.log", "w")

    while(1):
        resp = request_page(page)
        if len(resp.text) < 1:
           break # Finish when there is no new cell in web page

        (index,value,new) =  parse_resp(resp.text)
        TAB[int(index)] = value[2:-1] #Fill the tab

        print("retrieve:" + "".join(TAB),end="\r")
        page = new

        f.write("[%s,%s]\n%s\n\n" % (index,value, page)) #Write logs
        
    print("\n\nFinal TAB: " + "".join(TAB))

Here is what we retrieve

Step3: Flag it

The array look's like an hexdump of a file, we can try to decode it

Great ! this is a png file. And look at what was inside...

the flag: flag{automation_is_handy}

We are done, this was a really cool challenge.