【檔案上傳繞過】路徑拼接問題導致上傳漏洞

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一、原始碼

$is_upload = false;
$msg = null;
if (isset($_POST['submit'])) {
    if (file_exists(UPLOAD_PATH)) {
        $deny_ext = array(".php",".php5",".php4",".php3",".php2",".html",".htm",".phtml",".pht",".pHp",".pHp5",".pHp4",".pHp3",".pHp2",".Html",".Htm",".pHtml",".jsp",".jspa",".jspx",".jsw",".jsv",".jspf",".jtml",".jSp",".jSpx",".jSpa",".jSw",".jSv",".jSpf",".jHtml",".asp",".aspx",".asa",".asax",".ascx",".ashx",".asmx",".cer",".aSp",".aSpx",".aSa",".aSax",".aScx",".aShx",".aSmx",".cEr",".sWf",".swf",".htaccess");
        $file_name = trim($_FILES['upload_file']['name']);
        $file_name = deldot($file_name);//刪除檔名末尾的點
        $file_ext = strrchr($file_name, '.');
        $file_ext = strtolower($file_ext); //轉換為小寫
        $file_ext = str_ireplace('::$DATA', '', $file_ext);//去除字串::$DATA
        $file_ext = trim($file_ext); //首尾去空
        
        if (!in_array($file_ext, $deny_ext)) {
            $temp_file = $_FILES['upload_file']['tmp_name'];
            $img_path = UPLOAD_PATH.'/'.$file_name; // 路徑拼接的是處理後的檔名
            if (move_uploaded_file($temp_file, $img_path)) {
                $is_upload = true;
            } else {
                $msg = '上傳出錯！';
            }
        } else {
            $msg = '此檔案型別不允許上傳！';
        }
    } else {
        $msg = UPLOAD_PATH . '資料夾不存在,請手工建立！';
    }
}

路徑拼接的是處理後的檔名，導致可以利用類似.php. .(兩個點號之間有一個空格)繞過，程式先是刪除一個點，再刪除一個空格經過處理後，檔名變成.php.，即可繞過。

二、使用burpsuite修改檔案字尾繞過

上傳檔案並訪問

檔案上傳到Windows伺服器後會自動將後面的點去掉