Avatar Uploader

0x01关键代码

$finfo = finfo_open(FILEINFO_MIME_TYPE);
$type = finfo_file($finfo, $_FILES['file']['tmp_name']);
finfo_close($finfo);
if (!in_array($type, ['image/png'])) {
  error('Uploaded file is not PNG format.');
}



$size = getimagesize($_FILES['file']['tmp_name']);
if ($size[0] > 256 || $size[1] > 256) {
  error('Uploaded image is too large.');
}
if ($size[2] !== IMAGETYPE_PNG) {
  // I hope this never happens...
  error('What happened...? OK, the flag for part 1 is: <code>' . getenv('FLAG1') . '</code>');
}

函数finfo_file()其可以识别PNG文件十六进制的第一行信息，

破坏掉文件长宽等其余信息，也就可以绕过getimagesize() 函数的检验

Avatar Uploader_编程题

当返回的类型不为png时给出flag