170314 Social network VKontakte backdoor giving access to any personal files of any user without login

Never used VKontakte, but being curious of Russian representant to Eurovision 2017- Юлия САМОЙЛОВА  Julia SAMOYLOVA - I "visited" VKontakte.
So I discovered a "way" to access any file of any user, without login.
BURP Suite was used for traffic analysis.