89 lines
3.0 KiB
Python
89 lines
3.0 KiB
Python
"""
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A provided CSRF implementation which puts CSRF data in a session.
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This can be used fairly comfortably with many `request.session` type
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objects, including the Werkzeug/Flask session store, Django sessions, and
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potentially other similar objects which use a dict-like API for storing
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session keys.
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The basic concept is a randomly generated value is stored in the user's
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session, and an hmac-sha1 of it (along with an optional expiration time,
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for extra security) is used as the value of the csrf_token. If this token
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validates with the hmac of the random value + expiration time, and the
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expiration time is not passed, the CSRF validation will pass.
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"""
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from __future__ import unicode_literals
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import hmac
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import os
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from hashlib import sha1
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from datetime import datetime, timedelta
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from ..validators import ValidationError
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from .core import CSRF
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__all__ = ('SessionCSRF', )
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class SessionCSRF(CSRF):
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TIME_FORMAT = '%Y%m%d%H%M%S'
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def setup_form(self, form):
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self.form_meta = form.meta
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return super(SessionCSRF, self).setup_form(form)
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def generate_csrf_token(self, csrf_token_field):
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meta = self.form_meta
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if meta.csrf_secret is None:
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raise Exception('must set `csrf_secret` on class Meta for SessionCSRF to work')
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if meta.csrf_context is None:
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raise TypeError('Must provide a session-like object as csrf context')
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session = self.session
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if 'csrf' not in session:
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session['csrf'] = sha1(os.urandom(64)).hexdigest()
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if self.time_limit:
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expires = (self.now() + self.time_limit).strftime(self.TIME_FORMAT)
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csrf_build = '%s%s' % (session['csrf'], expires)
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else:
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expires = ''
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csrf_build = session['csrf']
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hmac_csrf = hmac.new(meta.csrf_secret, csrf_build.encode('utf8'), digestmod=sha1)
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return '%s##%s' % (expires, hmac_csrf.hexdigest())
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def validate_csrf_token(self, form, field):
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meta = self.form_meta
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if not field.data or '##' not in field.data:
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raise ValidationError(field.gettext('CSRF token missing'))
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expires, hmac_csrf = field.data.split('##', 1)
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check_val = (self.session['csrf'] + expires).encode('utf8')
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hmac_compare = hmac.new(meta.csrf_secret, check_val, digestmod=sha1)
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if hmac_compare.hexdigest() != hmac_csrf:
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raise ValidationError(field.gettext('CSRF failed'))
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if self.time_limit:
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now_formatted = self.now().strftime(self.TIME_FORMAT)
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if now_formatted > expires:
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raise ValidationError(field.gettext('CSRF token expired'))
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def now(self):
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"""
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Get the current time. Used for test mocking/overriding mainly.
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"""
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return datetime.now()
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@property
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def time_limit(self):
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return getattr(self.form_meta, 'csrf_time_limit', timedelta(minutes=30))
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@property
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def session(self):
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return getattr(self.form_meta.csrf_context, 'session', self.form_meta.csrf_context)
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