flask_Captchaify

A DDoS defense system for flask applications, first sends users to a captcha page without a javascript script and creates a confirmation cookie/url arg after the captcha.

Todos:

• Captcha type with images of emojis
• Captcha type with pictures of animals
• Captcha or blocking rules based on client_ip and client_ip_info (e.g. blocking of certain IP countries)

How does flask_Captchaify work?

If needed, a captcha is displayed to the user (or the robot) based on the strength set.¹ Javascript is not needed for this, as the content is rendered on the server.²

An example script could look like this:

from flask import Flask
from flask_Captchaify import Captcha

app = Flask(__name__)
captcha = Captcha(app, default_hardness=2, default_action = "fight")

@app.route("/")
def index():
    return 'Hello Human!'

if __name__ == "__main__":
    app.run(host = "localhost", port = 8080)

Tip

🎉 flask_Captchaify will soon have a new type of captcha Preview

Application purposes

A few application purposes:

• Protect against DDoS attacks ³
• Your website contains content that should not be read by a robot
• A login website
• A dark web page that simply needs to be secured a bit

Why should you use Captchaify if you host a Flask server?

A quick and easy implementation allows even small websites or a small team of developers to quickly get robot protection. It also doesn't use third-party providers, which limits data collection from Google, Facebook and the creepy data brokers.⁴ Everything is open source, meaning you can rewrite the code yourself and perhaps make it more private.

Instructions

Installation guide

1. Make sure you have the latest version of Python and Pip installed, you also need git installed.
2. Install the script with pip pip install flask_Captchaify or manually via git clone https://github.com/tn3w/flask_Captchaify or download the zip.
3. If you installed it manually, make sure your python script is in the folder where there is a subfolder flask_Captchaify, and make sure you run pip install -r requirements.txt in the flask_Captchaify folder.
4. Make sure that after:

   app = Flask(__name__)

   You add the line:

   captcha = Captcha(app, default_hardness=2, default_action = "fight")

   And at the beginning of the file add the import:

   from flask_Captchaify import Captcha

For more information, see the sample code above.

Personalization

1. actions Arg

   To change the response in the case of certain routes / endpoints, you can use the actions parameter.

   Example of a website that allows all bots on the main page, enforces captchas on the login page, and blocks all robots on the registration page:

   captcha = Captcha(app, actions={"/": "let", "/login": "fight", "/register": "block"})

   When using "*" before or after the urlpath / endpoint you can address multiple urls.

   Example of a website where all urls with /api/ are allowed through, all urls starting with "/dogs/" show everyone a captcha and all urls ending with "/cats/" block bots:

   captcha = Captcha(app, actions={"*/api/*": "let", "/dogs/*": "fight", "*/cats/": "block"})

   All actions:

   Name of action	Executing Action
   let	Allows all traffic through, regardless of whether the IP is blocked.
   block	Blocks all traffic if it is blocked, without captcha.
   fight	Displays a captcha to all traffic, whether suspicious or not.
   captcha	Default value, shows only suspicious traffic captchas.

   
   

2. hardness Arg

   To change the hardness of a captcha for specific routes or endpoints use hardness.

   Example of a website that sets the hardness of the main page to 1 (= easy), on the login page to 2 (= normal) and on the register page to 3 (= hard):

   captcha = Captcha(app, hardness={"/": 1, "/login": 2, "/register": 3})

   When using "*" before or after the urlpath / endpoint you can address multiple urls, like actions.

   All hardness levels:

   Hardness Level	Captcha modification
   1	The captcha is easy. Only a text captcha with 6 - 8 characters is displayed
   2	The captcha is normal. Only a text captcha with 9 - 11 characters is displayed
   3	The hardness of the captcha is hard, a 9 - 14 number audio captcha is displayed in addition to the 10 - 12 character text captcha.

   
   

3. rate_limits Arg

   To change the rate_limit and max_rate_limit for a specific route or endpoint use the rate_limits arg. The syntax is a bit different from the others, because two values are specified {"route": (rate_limit, max_rate_limit), "endpoint": (rate_limit, max_rate_limit)}. The variable rate_limit must be a number indicating how many requests per minute can come from a given ip. max_rate_limit indicates how many requests can come from all ips per minute, also a number.

   Example of a website that has a specific rate_limit on /api/:

   captcha = Captcha(app, template_dirs={"/api/*": (60, 600)})

   
   

4. template_dirs Arg

   To change the template directory of a particular route use the template_dirs arg.

   Example of a website that has a specific template directory on /api/:

   captcha = Captcha(app, template_dirs={"/api/*": "/path/to/special/template/directory"})

   A template directory can look like this:

   template_directory\
              \captcha.html
              \block.html
              \rate_limited.html
              \change_language.html
   

   If one of the three templates does not exist in the folder, a 404 error is displayed when calling it. e.g. if you remove the changelanguage page at apis.
   

5. default_action Arg

   To specify the default action of all routes or endpoints use the default_action arg.

   Example of a very paranoid website that has set its action to "fight" for all routes:

   captcha = Captcha(app, default_action="fight")

   
   

6. default_hardness Arg

   To specify the default hardness of all routes or endpoints use the default_hardness arg.

   Example of a very paranoid website that has set its hardness to 3 (= hard) for all routes:

   captcha = Captcha(app, default_hardness=3)

   
   

7. default_rate_limit Arg

   To specify the default requests of an IP per minute for all routes use the default_rate_limit variable. (Default: 120 = 2 requests per second per IP)

   Example of a web page with custom rate_limit:

   captcha = Captcha(app, default_rate_limit=60)

   
   

8. default_max_rate_limit Arg

   To specify the default requests of all IPs per minute for all routes use the default_max_rate_limit variable. (Default: 1200 = 2 requests per second from 10 IPs)

   Example of a web page with custom max_rate_limit:

   captcha = Captcha(app, default_max_rate_limit=600)

   
   

9. default_template_dir Arg

   To specify the default template_dir of all routes or endpoints use the default_template_dir arg.

   Example of a web page with custom template_dir:

   captcha = Captcha(app, default_template_dir="/path/to/my/custom/template/directory")

   
   

10. verification_age Arg

    Indicates the time in seconds how long a solved captcha is valid (Default: 3600 = 1 hour)

    Website with 3 hours verification_age:

    captcha = Captcha(app, verification_age=10800)

    
    

11. without_cookies Arg

    If True, no cookies are created, and verification is proven via URL args (Default: False)

    Website with without_cookies enabled:

    captcha = Captcha(app, without_cookies=True)

    
    

12. block_crawler Arg

    If True, crawlers like Googlebot, further are estimated via their user agent as suspicious and not the website, good for websites that should not be crawled (Default: True)

    Web page with block_crawler enabled:

    captcha = Captcha(app, block_crawler=True)

    
    

13. crawler_hints Arg:

    If True, crawlers like Googlebot, are shown meta tags and the title of a normal web page, while they would have to solve a captcha. (Default: True)

    Web page with crawler_hints disabled:

    captcha = Captcha(app, crawler_hints=False)

    
    

14. third_parties Arg:

    Specifies which third parties are used to check the IP addresses. By default, all 3 third parties are used. (See list)

    Web page that only asks a third party for Tor Ip addresses:

    captcha = Captcha(app, third_parties=["tor"])

    Possible entries would be:

    Abbreviation	Who is requested and how does the evaluation mechanism work?
    tor	SecOps-Institute/Tor-IP-Addresses on GitHub is asked for Tor Ipv4 and Ipv6 addresses and the Ip address is compared with this list
    ipapi	Ipapi is requested with the Ip and the result of the fields "proxy" and "hosting" is used
    stopforumspam	StopForumSpam is requested and the result is used

    
    

Footnotes

1. Text and, if the set strength is above 2, audio captchas can already be partially solved by robots, this is a solution for small websites or, e.g. dark web sites that cannot use third party solutions. However, it should still provide sufficient protection. ↩

2. For a captcha to work, however, the user's IP and user agent must normally be stored. The website may also collect data such as language to translate the website. Cookies can also be used, this is decided by the server administrator. ↩

3. Only if you have a large server that is supposed to protect a small server from DDoS attacks. ↩

4. Only if you do not use other services such as Google Analytics/Meta Pixel on your website. ↩