jean / plone.protect

HTTP protection utilities for the Plone CMS

Introduction

This package contains utilities that can help to protect parts of Plone or applications build on top of the Plone framework.

1. Restricting to HTTP POST

a) Using decorator

If you only need to allow HTTP POST requests you can use the PostOnly checker:

from plone.protect import PostOnly
from plone.protect import protect

@protect(PostOnly)
def manage_doSomething(self, param, REQUEST=None):
    pass

This checker only operates on HTTP requests; other types of requests are not checked.

b) Passing request to a function validator

Simply:

from plone.protect import PostOnly

...
PostOnly(self.context.REQUEST)
...

2. Form authentication (CSRF)

A common problem in web applications is Cross Site Request Forgery or CSRF. This is an attack method in which an attacker tricks a browser to do a HTTP form submit to another site. To do this the attacker needs to know the exact form parameters. Form authentication is a method to make it impossible for an attacker to predict those parameters by adding an extra authenticator which can be verified.

Generating the token

To use the form authenticator you first need to insert it into your form. This can be done using a simple TAL statement inside your form:

<span tal:replace="structure context/@@authenticator/authenticator"/>

this will produce a HTML input element with the authentication information.

Validating the token

a) ZCA way

Next you need to add logic somewhere to verify the authenticator. This can be done using a call to the authenticator view. For example:

authenticator=getMultiAdapter((context, request), name=u"authenticator")
if not authenticator.verify():
    raise Unauthorized

b) Using decorator

You can do the same thing more conveniently using the protect decorator:

from plone.protect import CheckAuthenticator
from plone.protect import protect

@protect(CheckAuthenticator)
def manage_doSomething(self, param, REQUEST=None):
    pass

c) Passing request to a function validator

Or just:

from plone.protect import CheckAuthenticator

...
CheckAuthenticator(self.context.REQUEST)
...

Headers

You can also pass in the token by using the header X-CSRF-TOKEN. This can be useful for AJAX requests.

Protect decorator

The most common way to use plone.protect is through the protect decorator. This decorator takes a list of checkers as parameters: each checker will check a specific security aspect of the request. For example:

from plone.protect import protect
from plone.protect import PostOnly

@protect(PostOnly)
def SensitiveMethod(self, REQUEST=None):
    # This is only allowed with HTTP POST requests.

This relies on the protected method having a parameter called REQUEST (case sensitive).

Customized Form Authentication

If you'd like use a different authentication token for different forms, you can provide an extra string to use with the token:

<tal:authenticator tal:define="authenticator context/@@authenticator">
  <span tal:replace="structure python: authenticator.authenticator('a-form-related-value')"/>
</tal:authenticator>

To verify:

authenticator=getMultiAdapter((context, request), name=u"authenticator")
if not authenticator.verify('a-form-related-value'):
    raise Unauthorized

With the decorator:

from plone.protect import CustomCheckAuthenticator
from plone.protect import protect

@protect(CustomCheckAuthenticator('a-form-related-value'))
def manage_doSomething(self, param, REQUEST=None):
    pass

Automatic CSRF Protection

Since version 3, plone.protect provides automatic CSRF protection. It does this by automatically including the auth token to all internal forms when the user requesting the page is logged in.

Additionally, whenever a particular request attempts to write to the ZODB, it'll check for the existence of a correct auth token.

Allowing write on read programatically

When you need to allow a known write on read, you've got several options.

Adding a CSRF token to your links

If you've got a GET request that causes a known write on read, your first option should be to simply add a CSRF token to the URLs that result in that request. plone.protect provides the addTokenToUrl function for this purpose:

from plone.protect.utils import addTokenToUrl

url = addTokenToUrl(url)

If you just want to allow an object to be writable on a request...

You can use the safeWrite helper function:

from plone.protect.auto import safeWrite

safeWrite(myobj, request)

Marking the entire request as safe

Just add the IDisableCSRFProtection interface to the current request object:

from plone.protect.interfaces import IDisableCSRFProtection
from zope.interface import alsoProvides

alsoProvides(request, IDisableCSRFProtection)

Warning! When you do this, the current request is susceptible to CSRF exploits so do any required CSRF protection manually.

Clickjacking Protection

plone.protect also provides, by default, clickjacking protection since version 3.0.

To protect against this attack, plone employs the use of the X-Frame-Options header. plone.protect will set the X-Frame-Options value to SAMEORIGIN.

To customize this value, you can set it to a custom value for a custom view (e.g. self.request.response.setHeader('X-Frame-Options', 'ALLOWALL')), override it at your proxy server, or you can set the environment variable of PLONE_X_FRAME_OPTIONS to whatever value you'd like plone.protect to set this to globally.

You can opt out of this by making the environment variable empty.

Disable All Automatic CSRF Protection

To disable all automatic CSRF protection, set the environment variable PLONE_CSRF_DISABLED value to true.

WARNING! It is very dangerous to do this. Do not do this unless the zeo client with this setting is not public and you know what you are doing.

Notes

This package monkey patches a number of modules in order to better handle CSRF protection:

- Archetypes add forms, add csrf
- Zope2 object locking support
- pluggable auth csrf protection