http://storeimage.whitehat.vn/s3rv1c3/?page=upload
POST : url=file:///proc/self/cwd/Fl4g.php

Upload image from url exist SSRF Vulnerability.we can use file:// protocol to read any file. ex: file:///etc/passwd. /proc/self/cwd This is a symbolic link to the current working directory. so /proc/self/cwd ==> /xxx/xxx/xxxx/s3rv1c3/ we read flag by file:///proc/self/cwd/Fl4g.php.