About this article

I will write a summary of what I did in the security department of the Computer Study Group for output. We will add more and more every Friday.

June 19

Activity content: I went to part3 and part4 of https://google-gruyere.appspot.com/.

Challenge: Creating a web application that allows you to experience Path Traversal Attack

`Directory structure`


.
├── templates
│   └── index.html
├── a.txt
├── b.txt
├── c.txt
├── pass.txt
└── app.py

`index.html`


<!doctype html>
<html lang="ja">

<head>
	<meta charset="utf-8">
	<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
	<title>Hello Jinja2</title>
</head>

<body>
	<h1>A web application that allows you to experience Path Traversal Attack</h1>
	<p>Please enter the file name of the file you want to display in the form below</p>
	<p><strong>a.txt</strong> <strong>b.txt</strong> <strong>c.txt</strong>You can choose from.</p>
	
	<form action="/" method="POST" enctype="multipart/form-data">
		<div>
			<label for="name">file name:</label>
			<input type="text" id="name" name="name" placeholder="name">
		</div>
		<div>
			<input type="submit" value="Send">
		</div>
	</form>
	<p>{{data}}</p>
	<br><br><br>
	<h4>Commentary</h4>
	<p>This site looks for a file with the received file name in the directory and returns it as is</p>
	<p>Therefore, there is a possibility that a confidential file will be returned when a file name that is not expected to be entered is entered.</p>
	<h3>pass.Let's enter txt</h3>
</body>

</html>

`a.txt`


This is a.The contents of txt.

`b.txt`


This is b.The contents of txt.

`c.txt`


This is c.The contents of txt.

`pass.txt`


I was able to extract valuable password data.

`app.py`


# -*- coding: utf-8 -*-
from flask import Flask, render_template, request

app = Flask(__name__)
	
@app.route('/', methods=['POST'])
def post():
	name = request.form.get('name')
	data = ""
	try:
		f = open(name)
		data = f.read()
		f.close()
	except:
		pass

	return render_template('index.html', data = data)

if __name__ == '__main__':
	app.run()

All I had to do was set up a local server, so I wrote it using Flask. It was ridiculously easy to implement, so it felt like Flask !. Is there really anyone who implements such a stupid vulnerability?

June 12

Activity content: I went to part0, part1, part2 of https://google-gruyere.appspot.com/.

What I learned: There are various types of XSS (cross-site scripting) such as reflective type, accumulation type, and DOM based xss. Take measures against XSS and sanitize (escape).

Challenge: Creating a web page where you can experience DOM Based XSS

`xss.html`


<html>
  <title>DOM Based XSS</title>
  <h1>A site where you can experience DOM Based XSS</h1>
  Hi
  <script charset="UTF-8">
    var pos=document.URL.indexOf("name=")+5;
    document.write(unescape(document.URL.substring(pos,document.URL.length)));
  </script>
  <br><br>
  <p>If you give a name as a parameter at the end of the url of this page, it will dynamically rewrite the html</p>
  <p>(Example) 〜〜xss.html?name=Taro</p>
  <p>I think the name is displayed after Hi at the top.</p><br>
  <P>However, this site will execute it when a malicious script is put in the parameter.</P>
  <p>(Example) 〜〜xss.html?name=&ltscript&gtalert("Your PC was broken!!")&lt/script&gt</p>
  <P>Being able to alert will cause you to run a script that actually has a negative effect.</P>
  </html>

[JAVA] Activity record in the programming circle

About this article

June 19

Directory structure

index.html

a.txt

b.txt

c.txt

pass.txt

app.py