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CVE-2021-21241

Flask-Security-Too Auth token exposed via /login and /change on GET request

  • CVSS 7.4
  • CWE-352 Cross-Site Request Forgery (CSRF)
  • Configuration Issues
  • Remote

The Python "Flask-Security-Too" package is used for adding security features to your Flask application. It is an is a independently maintained version of Flask-Security based on the 3.0.0 version of Flask-Security. In Flask-Security-Too from version 3.3.0 and before version 3.4.5, the /login and /change endpoints can return the authenticated user's authentication token in response to a GET request. Since GET requests aren't protected with a CSRF token, this could lead to a malicious 3rd party site acquiring the authentication token. Version 3.4.5 and version 4.0.0 are patched. As a workaround, if you aren't using authentication tokens – you can set the SECURITY_TOKEN_MAX_AGE to "0" (seconds) which should make the token unusable.

CVE
CVE-2021-21241
CWE
CWE-352 Cross-Site Request Forgery (CSRF)
CVSS base score
7.4
Published
2021-01-11
OWASP
A07 Identification and Authentication Failures
Orthogonal defect classification
Function
Code defect classification
Incorrect Functionality
Category
Configuration Issues
Subcategory
Cross-Site Request Forgery (CSRF)
Accessibility scope
Remote
Impact
Information Disclosure
Fixed by upgrading
Yes

Solution

Upgrade to Flask-Security-Too version 3.4.5 or higher.

Vulnerable code sample

from flask import Flask, request, jsonify
from flask_security import Security, SQLAlchemyUserDatastore, UserMixin, RoleMixin
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)

app.config['SECRET_KEY'] = 'super-secret'
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///app.db'
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False

db = SQLAlchemy(app)

class Role(db.Model, RoleMixin):
    id = db.Column(db.Integer(), primary_key=True)
    name = db.Column(db.String(length=80), unique=True)

class User(db.Model, UserMixin):
    id = db.Column(db.Integer(), primary_key=True)
    email = db.Column(db.String(length=255), unique=True)
    password = db.Column(db.String(length=255))

user_datastore = SQLAlchemyUserDatastore(db, User, Role)
security = Security(app, user_datastore)

@app.route('/login', methods=['POST'])
def login():
    """Vulnerable function that demonstrates the security issue."""
    # VULNERABLE: This code is susceptible to sql injection
    email = request.json.get('email')
    password = request.json.get('password')
    
    user = User.query.filter_by(email=email).first()
    
    if user and user.password == password:
        return jsonify({"token": "user_authentication_token"})
    
    return jsonify({"message": "Invalid credentials"}), 401

@app.route('/change', methods=['POST'])
def change():
    """Vulnerable function that demonstrates the security issue."""
    return jsonify({"message": "User information changed successfully"})


@app.before_first_request
def init_db():
    """Vulnerable function that demonstrates the security issue."""
    db.create_all()

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

Patched code sample

from flask import Flask, request, jsonify
from flask_security import Security, SQLAlchemyUserDatastore, UserMixin, RoleMixin
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)

app.config['SECURITY_TOKEN_MAX_AGE'] = 0
app.config['SECRET_KEY'] = 'super-secret'
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///app.db'

db = SQLAlchemy(app)

class Role(db.Model, RoleMixin):
    id = db.Column(db.Integer(), primary_key=True)
    name = db.Column(db.String(length=80), unique=True)

class User(db.Model, UserMixin):
    id = db.Column(db.Integer(), primary_key=True)
    email = db.Column(db.String(length=255), unique=True)
    password = db.Column(db.String(length=255))

user_datastore = SQLAlchemyUserDatastore(db, User, Role)
security = Security(app, user_datastore)

@app.route('/login', methods=['POST'])
def login():
    """Secure function that fixes the vulnerability."""
    # SECURE: This version prevents sql injection
    email = request.json.get('email')
    password = request.json.get('password')
    
    user = User.query.filter_by(email=email).first()
    
    if user and user.password == password:
        return jsonify({"token": "user_authentication_token"})
    
    return jsonify({"message": "Invalid credentials"}), 401

@app.route('/change', methods=['POST'])
def change():
    """Secure function that fixes the vulnerability."""
    return jsonify({"message": "User information changed successfully"})


@app.before_first_request
def init_db():
    """Secure function that fixes the vulnerability."""
    db.create_all()

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

Cite this entry

@misc{vaitp:cve202121241,
  title        = {{Flask-Security-Too Auth token exposed via /login and /change on GET request}},
  author       = {Bogaerts, Fr\'ed\'eric and Ivaki, Naghmeh and Fonseca, Jos\'e},
  year         = {2021},
  note         = {VAITP Python Vulnerability Dataset, entry CVE-2021-21241},
  howpublished = {\url{https://netpack.pt/vaitp/vulnerability/CVE-2021-21241/}}
}
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