Bug in POST-request

[r0hack]

• PHP version: PHP/7.1.3
• Webserver (Nginx, Apache...): nginx/1.16.0

Hi. An error occurs and error output during transmission % and 2 symbols in parameter admin_user

Request: POST /index.php?admin HTTP/1.1
Body: admin_username=admin'%bf&admin_pass=pass&admin_login=Login
Response: http://prntscr.com/nxf663