DVWA-XSS(Stored)

Low

观察后端代码，对输入进行了一些过滤和转义。trim(string,charlist) 函数用于移除字符串两侧的空白字符或其他预定义字符，charlist 参数可以规定从字符串中删除哪些字符。stripslashes() 函数用于删除反斜杠。mysqli_real_escape_string() 函数用于对字符串中的特殊字符进行转义，使得这个字符串是一个合法的 SQL 语句。

<?phpif( isset( $_POST[ 'btnSign' ] ) ) {// Get input$message = trim( $_POST[ 'mtxMessage' ] );$name    = trim( $_POST[ 'txtName' ] );// Sanitize message input$message = stripslashes( $message );$message = ((isset($GLOBALS["___mysqli_ston"]) && is_object($GLOBALS["___mysqli_ston"])) ? mysqli_real_escape_string($GLOBALS["___mysqli_ston"],  $message ) : ((trigger_error("[MySQLConverterToo] Fix the mysql_escape_string() call! This code does not work.", E_USER_ERROR)) ? "" : ""));// Sanitize name input$name = ((isset($GLOBALS["___mysqli_ston"]) && is_object($GLOBALS["___mysqli_ston"])) ? mysqli_real_escape_string($GLOBALS["___mysqli_ston"],  $name ) : ((trigger_error("[MySQLConverterToo] Fix the mysql_escape_string() call! This code does not work.", E_USER_ERROR)) ? "" : ""));// Update database$query  = "INSERT INTO guestbook ( comment, name ) VALUES ( '$message', '$name' );";$result = mysqli_query($GLOBALS["___mysqli_ston"],  $query ) or die( '<pre>' . ((is_object($GLOBALS["___mysqli_ston"])) ? mysqli_error($GLOBALS["___mysqli_ston"]) : (($___mysqli_res = mysqli_connect_error()) ? $___mysqli_res : false)) . '</pre>' );//mysql_close();
}?>

我们直接进行XSS注入

Medium

在Low的基础上，message处理增加了strip_tags(addslashes())和htmlspecialchars()，其中addslashes函数添加反斜杠转义单引号、双引号、反斜杠和 NULL 字符。strip_tags函数删除字符串中的所有 HTML 标签。htmlspecialchars 函数将参数中的特殊字符（如 <, >, &, " 等）转换为 HTML 实体；name处增加了对<script>的过滤。

<?phpif( isset( $_POST[ 'btnSign' ] ) ) {// Get input$message = trim( $_POST[ 'mtxMessage' ] );$name    = trim( $_POST[ 'txtName' ] );// Sanitize message input$message = strip_tags( addslashes( $message ) );$message = ((isset($GLOBALS["___mysqli_ston"]) && is_object($GLOBALS["___mysqli_ston"])) ? mysqli_real_escape_string($GLOBALS["___mysqli_ston"],  $message ) : ((trigger_error("[MySQLConverterToo] Fix the mysql_escape_string() call! This code does not work.", E_USER_ERROR)) ? "" : ""));$message = htmlspecialchars( $message );// Sanitize name input$name = str_replace( '<script>', '', $name );$name = ((isset($GLOBALS["___mysqli_ston"]) && is_object($GLOBALS["___mysqli_ston"])) ? mysqli_real_escape_string($GLOBALS["___mysqli_ston"],  $name ) : ((trigger_error("[MySQLConverterToo] Fix the mysql_escape_string() call! This code does not work.", E_USER_ERROR)) ? "" : ""));// Update database$query  = "INSERT INTO guestbook ( comment, name ) VALUES ( '$message', '$name' );";$result = mysqli_query($GLOBALS["___mysqli_ston"],  $query ) or die( '<pre>' . ((is_object($GLOBALS["___mysqli_ston"])) ? mysqli_error($GLOBALS["___mysqli_ston"]) : (($___mysqli_res = mysqli_connect_error()) ? $___mysqli_res : false)) . '</pre>' );//mysql_close();
}
?>

我们发现name处可以进绕过，name参数长度有限制，可以直接修改前端代码，也可以burp抓包后修改参数

High

和XSS(Reflected) high level一样，在Medium基础上<script>标签被完全过滤。但是我们可以通过其他的标签例如 img、body 等标签的事件注入。
参考XSS Payload List

Impossible

在High的基础上增加了对name参数的严格过滤，并且加入了token机制。

<?phpif( isset( $_POST[ 'btnSign' ] ) ) {// Check Anti-CSRF tokencheckToken( $_REQUEST[ 'user_token' ], $_SESSION[ 'session_token' ], 'index.php' );// Get input$message = trim( $_POST[ 'mtxMessage' ] );$name    = trim( $_POST[ 'txtName' ] );// Sanitize message input$message = stripslashes( $message );$message = ((isset($GLOBALS["___mysqli_ston"]) && is_object($GLOBALS["___mysqli_ston"])) ? mysqli_real_escape_string($GLOBALS["___mysqli_ston"],  $message ) : ((trigger_error("[MySQLConverterToo] Fix the mysql_escape_string() call! This code does not work.", E_USER_ERROR)) ? "" : ""));$message = htmlspecialchars( $message );// Sanitize name input$name = stripslashes( $name );$name = ((isset($GLOBALS["___mysqli_ston"]) && is_object($GLOBALS["___mysqli_ston"])) ? mysqli_real_escape_string($GLOBALS["___mysqli_ston"],  $name ) : ((trigger_error("[MySQLConverterToo] Fix the mysql_escape_string() call! This code does not work.", E_USER_ERROR)) ? "" : ""));$name = htmlspecialchars( $name );// Update database$data = $db->prepare( 'INSERT INTO guestbook ( comment, name ) VALUES ( :message, :name );' );$data->bindParam( ':message', $message, PDO::PARAM_STR );$data->bindParam( ':name', $name, PDO::PARAM_STR );$data->execute();
}// Generate Anti-CSRF token
generateSessionToken();?>

防御

1.过滤输入的字符，例如 “ ’ ”，“ " ”，“<”，“>” 等非法字符；
2.对输入到页面的数据进行编码