robsware

The vulnerability is Unrestricted Upload of File with Dangerous Type

from flask import Flask, request

app = Flask(__name__)

@app.route('/')
def index():
    return '''
        <html>
            <body>
                <form action="/upload" method="post" enctype="multipart/form-data">
                    <input type="file" name="file">
                    <input type="submit" value="Upload">
                </form>
            </body>
        </html>
    '''

@app.route('/upload', methods=['POST'])
def upload_file():
    uploaded_file = request.files['file']
    uploaded_file.save(uploaded_file.filename)
    return 'File uploaded successfully.'

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

The above code is vulnerable to Unrestricted Upload of File with Dangerous Type, as it doesn't check if the uploaded file is of a safe type or not. An attacker can abuse this vulnerability by uploading a malicious file with an executable extension such as .exe, .py, .sh, etc. which can lead to remote code execution. To fix this vulnerability, we can check the file's extension to ensure it is of an allowed type. We can do this by creating a set of allowed extensions and checking if the uploaded file's extension is present in the set. Here is an example:

import os
from flask import Flask, request

app = Flask(__name__)

ALLOWED_EXTENSIONS = {'txt', 'pdf', 'png', 'jpg', 'jpeg', 'gif'}

def allowed_file(filename):
    return '.' in filename and \
           filename.rsplit('.', 1)[1].lower() in ALLOWED_EXTENSIONS

@app.route('/upload', methods=['POST'])
def upload_file():
    uploaded_file = request.files['file']
    if uploaded_file.filename == '':
        return 'No file selected.'
    if uploaded_file and allowed_file(uploaded_file.filename):
        # This line saves the file to the current working directory
        uploaded_file.save(uploaded_file.filename)
        return 'File uploaded successfully.'
    else:
        return 'Invalid file type.'

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