330 lines
9.9 KiB
Python
330 lines
9.9 KiB
Python
import hashlib
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import hmac
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import logging
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import os
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from urllib.parse import urlparse
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from flask import Blueprint
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from flask import current_app
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from flask import g
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from flask import request
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from flask import session
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from itsdangerous import BadData
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from itsdangerous import SignatureExpired
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from itsdangerous import URLSafeTimedSerializer
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from werkzeug.exceptions import BadRequest
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from wtforms import ValidationError
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from wtforms.csrf.core import CSRF
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__all__ = ("generate_csrf", "validate_csrf", "CSRFProtect")
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logger = logging.getLogger(__name__)
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def generate_csrf(secret_key=None, token_key=None):
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"""Generate a CSRF token. The token is cached for a request, so multiple
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calls to this function will generate the same token.
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During testing, it might be useful to access the signed token in
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``g.csrf_token`` and the raw token in ``session['csrf_token']``.
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:param secret_key: Used to securely sign the token. Default is
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``WTF_CSRF_SECRET_KEY`` or ``SECRET_KEY``.
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:param token_key: Key where token is stored in session for comparison.
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Default is ``WTF_CSRF_FIELD_NAME`` or ``'csrf_token'``.
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"""
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secret_key = _get_config(
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secret_key,
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"WTF_CSRF_SECRET_KEY",
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current_app.secret_key,
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message="A secret key is required to use CSRF.",
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)
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field_name = _get_config(
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token_key,
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"WTF_CSRF_FIELD_NAME",
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"csrf_token",
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message="A field name is required to use CSRF.",
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)
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if field_name not in g:
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s = URLSafeTimedSerializer(secret_key, salt="wtf-csrf-token")
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if field_name not in session:
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session[field_name] = hashlib.sha1(os.urandom(64)).hexdigest()
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try:
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token = s.dumps(session[field_name])
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except TypeError:
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session[field_name] = hashlib.sha1(os.urandom(64)).hexdigest()
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token = s.dumps(session[field_name])
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setattr(g, field_name, token)
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return g.get(field_name)
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def validate_csrf(data, secret_key=None, time_limit=None, token_key=None):
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"""Check if the given data is a valid CSRF token. This compares the given
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signed token to the one stored in the session.
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:param data: The signed CSRF token to be checked.
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:param secret_key: Used to securely sign the token. Default is
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``WTF_CSRF_SECRET_KEY`` or ``SECRET_KEY``.
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:param time_limit: Number of seconds that the token is valid. Default is
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``WTF_CSRF_TIME_LIMIT`` or 3600 seconds (60 minutes).
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:param token_key: Key where token is stored in session for comparison.
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Default is ``WTF_CSRF_FIELD_NAME`` or ``'csrf_token'``.
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:raises ValidationError: Contains the reason that validation failed.
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.. versionchanged:: 0.14
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Raises ``ValidationError`` with a specific error message rather than
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returning ``True`` or ``False``.
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"""
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secret_key = _get_config(
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secret_key,
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"WTF_CSRF_SECRET_KEY",
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current_app.secret_key,
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message="A secret key is required to use CSRF.",
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)
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field_name = _get_config(
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token_key,
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"WTF_CSRF_FIELD_NAME",
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"csrf_token",
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message="A field name is required to use CSRF.",
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)
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time_limit = _get_config(time_limit, "WTF_CSRF_TIME_LIMIT", 3600, required=False)
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if not data:
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raise ValidationError("The CSRF token is missing.")
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if field_name not in session:
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raise ValidationError("The CSRF session token is missing.")
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s = URLSafeTimedSerializer(secret_key, salt="wtf-csrf-token")
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try:
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token = s.loads(data, max_age=time_limit)
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except SignatureExpired as e:
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raise ValidationError("The CSRF token has expired.") from e
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except BadData as e:
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raise ValidationError("The CSRF token is invalid.") from e
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if not hmac.compare_digest(session[field_name], token):
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raise ValidationError("The CSRF tokens do not match.")
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def _get_config(
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value, config_name, default=None, required=True, message="CSRF is not configured."
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):
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"""Find config value based on provided value, Flask config, and default
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value.
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:param value: already provided config value
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:param config_name: Flask ``config`` key
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:param default: default value if not provided or configured
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:param required: whether the value must not be ``None``
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:param message: error message if required config is not found
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:raises KeyError: if required config is not found
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"""
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if value is None:
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value = current_app.config.get(config_name, default)
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if required and value is None:
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raise RuntimeError(message)
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return value
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class _FlaskFormCSRF(CSRF):
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def setup_form(self, form):
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self.meta = form.meta
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return super().setup_form(form)
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def generate_csrf_token(self, csrf_token_field):
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return generate_csrf(
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secret_key=self.meta.csrf_secret, token_key=self.meta.csrf_field_name
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)
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def validate_csrf_token(self, form, field):
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if g.get("csrf_valid", False):
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# already validated by CSRFProtect
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return
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try:
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validate_csrf(
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field.data,
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self.meta.csrf_secret,
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self.meta.csrf_time_limit,
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self.meta.csrf_field_name,
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)
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except ValidationError as e:
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logger.info(e.args[0])
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raise
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class CSRFProtect:
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"""Enable CSRF protection globally for a Flask app.
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::
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app = Flask(__name__)
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csrf = CSRFProtect(app)
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Checks the ``csrf_token`` field sent with forms, or the ``X-CSRFToken``
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header sent with JavaScript requests. Render the token in templates using
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``{{ csrf_token() }}``.
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See the :ref:`csrf` documentation.
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"""
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def __init__(self, app=None):
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self._exempt_views = set()
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self._exempt_blueprints = set()
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if app:
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self.init_app(app)
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def init_app(self, app):
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app.extensions["csrf"] = self
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app.config.setdefault("WTF_CSRF_ENABLED", True)
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app.config.setdefault("WTF_CSRF_CHECK_DEFAULT", True)
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app.config["WTF_CSRF_METHODS"] = set(
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app.config.get("WTF_CSRF_METHODS", ["POST", "PUT", "PATCH", "DELETE"])
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)
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app.config.setdefault("WTF_CSRF_FIELD_NAME", "csrf_token")
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app.config.setdefault("WTF_CSRF_HEADERS", ["X-CSRFToken", "X-CSRF-Token"])
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app.config.setdefault("WTF_CSRF_TIME_LIMIT", 3600)
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app.config.setdefault("WTF_CSRF_SSL_STRICT", True)
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app.jinja_env.globals["csrf_token"] = generate_csrf
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app.context_processor(lambda: {"csrf_token": generate_csrf})
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@app.before_request
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def csrf_protect():
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if not app.config["WTF_CSRF_ENABLED"]:
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return
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if not app.config["WTF_CSRF_CHECK_DEFAULT"]:
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return
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if request.method not in app.config["WTF_CSRF_METHODS"]:
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return
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if not request.endpoint:
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return
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if app.blueprints.get(request.blueprint) in self._exempt_blueprints:
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return
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view = app.view_functions.get(request.endpoint)
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dest = f"{view.__module__}.{view.__name__}"
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if dest in self._exempt_views:
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return
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self.protect()
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def _get_csrf_token(self):
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# find the token in the form data
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field_name = current_app.config["WTF_CSRF_FIELD_NAME"]
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base_token = request.form.get(field_name)
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if base_token:
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return base_token
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# if the form has a prefix, the name will be {prefix}-csrf_token
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for key in request.form:
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if key.endswith(field_name):
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csrf_token = request.form[key]
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if csrf_token:
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return csrf_token
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# find the token in the headers
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for header_name in current_app.config["WTF_CSRF_HEADERS"]:
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csrf_token = request.headers.get(header_name)
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if csrf_token:
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return csrf_token
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return None
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def protect(self):
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if request.method not in current_app.config["WTF_CSRF_METHODS"]:
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return
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try:
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validate_csrf(self._get_csrf_token())
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except ValidationError as e:
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logger.info(e.args[0])
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self._error_response(e.args[0])
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if request.is_secure and current_app.config["WTF_CSRF_SSL_STRICT"]:
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if not request.referrer:
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self._error_response("The referrer header is missing.")
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good_referrer = f"https://{request.host}/"
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if not same_origin(request.referrer, good_referrer):
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self._error_response("The referrer does not match the host.")
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g.csrf_valid = True # mark this request as CSRF valid
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def exempt(self, view):
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"""Mark a view or blueprint to be excluded from CSRF protection.
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::
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@app.route('/some-view', methods=['POST'])
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@csrf.exempt
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def some_view():
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...
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::
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bp = Blueprint(...)
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csrf.exempt(bp)
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"""
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if isinstance(view, Blueprint):
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self._exempt_blueprints.add(view)
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return view
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if isinstance(view, str):
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view_location = view
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else:
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view_location = ".".join((view.__module__, view.__name__))
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self._exempt_views.add(view_location)
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return view
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def _error_response(self, reason):
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raise CSRFError(reason)
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class CSRFError(BadRequest):
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"""Raise if the client sends invalid CSRF data with the request.
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Generates a 400 Bad Request response with the failure reason by default.
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Customize the response by registering a handler with
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:meth:`flask.Flask.errorhandler`.
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"""
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description = "CSRF validation failed."
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def same_origin(current_uri, compare_uri):
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current = urlparse(current_uri)
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compare = urlparse(compare_uri)
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return (
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current.scheme == compare.scheme
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and current.hostname == compare.hostname
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and current.port == compare.port
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)
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