Whenever you are accepting or asking users to input data to your application there comes an added responsibility that it should be done as safely as possible. Below outlines the things to consider when building your forms.
Cross-Site request forgery (CSRF)
Silverstripe CMS protects users against Cross-Site Request Forgery
CSRF) by adding a
SecurityID HiddenField to each Form instance. The
SecurityID contains a
random string generated by SecurityToken to identify the particular user request vs a third-party forging fake
SecurityToken automatically added looks something like:
use SilverStripe\Forms\Form; $form = Form::create(/* ... */); echo $form->getSecurityToken()->getValue(); // 'c443076989a7f24cf6b35fe1360be8683a753e2c'
This token value is passed through the rendered Form HTML as a HiddenField.
<input type="hidden" name="SecurityID" value="c443076989a7f24cf6b35fe1360be8683a753e2c" class="hidden" />
The token should be present whenever a operation has a side effect such as a
It can be safely disabled for
GET requests as long as it does not modify the database (i.e. a search form does not
normally require a security token).
$form = Form::create(/* ... */); $form->disableSecurityToken();
SecurityIDfor forms that perform some modification to the user's session. This will open your application up to
Strict form submission
To reduce attack exposure forms are limited, by default, to the intended HTTP verb (mostly
this check, forms that rely on
GET can be submitted via
PUT or vice-versa potentially leading to
application errors or edge cases. If you need to disable this setting follow the below example:
$form = Form::create(/* ... */); $form->setFormMethod('POST'); $form->setStrictFormMethodCheck(false); // or alternative short notation.. $form->setFormMethod('POST', false);
Spam and bot attacks
Silverstripe CMS has no built-in protection for detailing with bots, captcha or other spam protection methods. This
functionality is available as an additional Spam Protection
module if required. The module provides an consistent API for allowing third-party spam protection handlers such as
Recaptcha to work within the
Data disclosure through HTTP caching
Forms, and particularly their responses, can contain sensitive or user-specific data.
Forms can prepopulate submissions when a form is redisplayed with validation errors,
and they by default contain CSRF tokens unique to the user's session.
This data can inadvertently be stored either in a user's browser cache or in an intermediary
cache such as a CDN or other caching-proxy. If incorrect
Cache-Control headers are used, private data may be cached and
accessible publicly through the CDN.
To ensure this doesn't happen Silverstripe CMS adds
Cache-Control: no-store, no-cache, must-revalidate headers to any
forms that have validators or security tokens (all of them by default) applied to them; this ensures that CDNs
(and browsers) will not cache these pages.
See Performance: HTTP Cache Headers.