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.