20 KiB
Security
Introduction
This page details notes on how to ensure that we develop secure SilverStripe applications. See our "Release Process on how to report security issues.
SQL Injection
The coding-conventions help guard against SQL injection attacks but still require developer diligence: ensure that any variable you insert into a filter / sort / join clause has been escaped.
See http://shiflett.org/articles/sql-injection.
Automatic escaping
SilverStripe automatically escapes data in SQL statements wherever possible,
through database-specific methods (see [api:Database->addslashes()]).
For [api:MySQLDatabase], this will be [mysql_real_escape_string()](http://de3.php.net/mysql_real_escape_string).
- Most
[api:DataList]accessors (see escaping note in method documentation) - DataObject::get_by_id()
- DataObject::update()
- DataObject::castedUpdate()
- DataObject->Property = 'val', DataObject->setField('Property','val')
- DataObject::write()
- DataList->byID()
- Form->saveInto()
- FormField->saveInto()
- DBField->saveInto()
Data is escaped when saving back to the database, not when writing to object-properties.
Example:
:::php
// automatically escaped/quoted
$members = Member::get()->filter('Name', $_GET['name']);
// automatically escaped/quoted
$members = Member::get()->filter(array('Name' => $_GET['name']));
// needs to be escaped/quoted manually
$members = Member::get()->where(sprintf('"Name" = \'%s\'', Convert::raw2sql($_GET['name'])));
Manual escaping
As a rule of thumb, whenever you're creating raw queries (or just chunks of SQL), you need to take care of escaping yourself. See coding-conventions and datamodel for ways to cast and convert your data.
SQLQueryDataObject::buildSQL()DB::query()Director::urlParams()Controller->requestParams,Controller->urlParamsSS_HTTPRequestdata- GET/POST data passed to a form method
Example:
:::php
class MyForm extends Form {
public function save($RAW_data, $form) {
$SQL_data = Convert::raw2sql($RAW_data); // works recursively on an array
$objs = Player::get()->where("Name = '{$SQL_data[name]}'");
// ...
}
}
FormField->Value()- URLParams passed to a Controller-method
Example:
:::php
class MyController extends Controller {
private static $allowed_actions = array('myurlaction');
public function myurlaction($RAW_urlParams) {
$SQL_urlParams = Convert::raw2sql($RAW_urlParams); // works recursively on an array
$objs = Player::get()->where("Name = '{$SQL_data[OtherID]}'");
// ...
}
}
As a rule of thumb, you should escape your data as close to querying as possible. This means if you've got a chain of functions passing data through, escaping should happen at the end of the chain.
:::php
class MyController extends Controller {
/**
* @param array $RAW_data All names in an indexed array (not SQL-safe)
*/
public function saveAllNames($RAW_data) {
// $SQL_data = Convert::raw2sql($RAW_data); // premature escaping
foreach($RAW_data as $item) $this->saveName($item);
}
public function saveName($RAW_name) {
$SQL_name = Convert::raw2sql($RAW_name);
DB::query("UPDATE Player SET Name = '{$SQL_name}'");
}
}
This might not be applicable in all cases - especially if you are building an API thats likely to be customized. If you're passing unescaped data, make sure to be explicit about it by writing phpdoc-documentation and prefixing your variables ($RAW_data instead of $data).
XSS (Cross-Site-Scripting)
SilverStripe helps you guard any output against clientside attacks initiated by malicious user input, commonly known as XSS (Cross-Site-Scripting). With some basic guidelines, you can ensure your output is safe for a specific use case (e.g. displaying a blog post in HTML from a trusted author, or escaping a search parameter from an untrusted visitor before redisplaying it).
See http://shiflett.org/articles/foiling-cross-site-attacks for in-depth information about "Cross-Site-Scripting".
What if I can't trust my editors?
The default configuration of SilverStripe assumes some level of trust is given to your editors who have access to the CMS. Though the HTML WYSIWYG editor is configured to provide some control over the HTML an editor provides, this is not enforced server side, and so can be bypassed by a malicious editor. A editor that does so can use an XSS attack against an admin to perform any administrative action.
If you can't trust your editors, SilverStripe must be configured to filter the content so that any javascript is stripped out
To enable filtering, set the HtmlEditorField::$sanitise_server_side configuration property to true, e.g.
HtmlEditorField::config()->sanitise_server_side = true
The built in sanitiser enforces the TinyMCE whitelist rules on the server side, and is sufficient to eliminate the most common XSS vectors.
However some subtle XSS attacks that exploit HTML parsing bugs need heavier filtering. For greater protection you can install the htmlpurifier module which will replace the built in sanitiser with one that uses the HTML Purifier library. In both cases, you must ensure that you have not configured TinyMCE to explicitly allow script elements or other javascript-specific attributes.
For HTMLText database fields which aren't edited through HtmlEditorField, you also
have the option to explicitly whitelist allowed tags in the field definition, e.g. "MyField" => "HTMLText('meta','link')".
The SiteTree.ExtraMeta property uses this to limit allowed input.
But I also need my editors to provide javascript
It is not currently possible to allow editors to provide javascript content and yet still protect other users from any malicious code within that javascript.
We recommend configuring shortcodes that can be used by editors in place of using javascript directly.
Escaping model properties
[api:SSViewer] (the SilverStripe template engine) automatically takes care of escaping HTML tags from specific
object-properties by casting its string value into a [api:DBField] object.
PHP:
:::php
class MyObject extends DataObject {
private static $db = array(
'MyEscapedValue' => 'Text', // Example value: <b>not bold</b>
'MyUnescapedValue' => 'HTMLText' // Example value: <b>bold</b>
);
}
Template:
:::php
<ul>
<li>$MyEscapedValue</li> // output: <b>not bold<b>
<li>$MyUnescapedValue</li> // output: <b>bold</b>
</ul>
The example below assumes that data wasn't properly filtered when saving to the database, but are escaped before outputting through SSViewer.
Overriding default escaping in templates
You can force escaping on a casted value/object by using an escape type method in your template, e.g. "XML" or "ATT".
Template (see above):
:::php
<ul>
// output: <a href="#" title="foo & &#quot;bar"">foo & "bar"</a>
<li><a href="#" title="$Title.ATT">$Title</a></li>
<li>$MyEscapedValue</li> // output: <b>not bold<b>
<li>$MyUnescapedValue</li> // output: <b>bold</b>
<li>$MyUnescapedValue.XML</li> // output: <b>bold<b>
</ul>
Escaping custom attributes and getters
Every object attribute or getter method used for template purposes should have its escape type defined through the static $casting array. Caution: Casting only applies when using values in a template, not in PHP.
PHP:
:::php
class MyObject extends DataObject {
public $Title = '<b>not bold</b>'; // will be escaped due to Text casting
$casting = array(
"Title" => "Text", // forcing a casting
'TitleWithHTMLSuffix' => 'HTMLText' // optional, as HTMLText is the default casting
);
public function TitleWithHTMLSuffix($suffix) {
// $this->Title is not casted in PHP
return $this->Title . '<small>(' . $suffix. ')</small>';
}
}
Template:
:::php
<ul>
<li>$Title</li> // output: <b>not bold<b>
<li>$Title.RAW</li> // output: <b>not bold</b>
<li>$TitleWithHTMLSuffix</li> // output: <b>not bold</b>: <small>(...)</small>
</ul>
Note: Avoid generating HTML by string concatenation in PHP wherever possible to minimize risk and separate your presentation from business logic.
Manual escaping in PHP
When using customise() or renderWith() calls in your controller, or otherwise forcing a custom context for your template, you'll need to take care of casting and escaping yourself in PHP.
The [api:Convert] class has utilities for this, mainly Convert::raw2xml() and Convert::raw2att() (which is
also used by XML and ATT in template code).
PHP:
:::php
class MyController extends Controller {
private static $allowed_actions = array('search');
public function search($request) {
$htmlTitle = '<p>Your results for:' . Convert::raw2xml($request->getVar('Query')) . '</p>';
return $this->customise(array(
'Query' => Text::create($request->getVar('Query')),
'HTMLTitle' => HTMLText::create($htmlTitle)
));
}
}
Template:
:::php
<h2 title="Searching for $Query.ATT">$HTMLTitle</h2>
Whenever you insert a variable into an HTML attribute within a template, use $VarName.ATT, no not $VarName.
You can also use the built-in casting in PHP by using the obj() wrapper, see datamodel .
Escaping URLs
Whenever you are generating a URL that contains querystring components based on user data, use urlencode() to escape the user data, not Convert::raw2att(). Use raw ampersands in your URL, and cast the URL as a "Text" DBField:
PHP:
:::php
class MyController extends Controller {
private static $allowed_actions = array('search');
public function search($request) {
$rssRelativeLink = "/rss?Query=" . urlencode($_REQUEST['query']) . "&sortOrder=asc";
$rssLink = Controller::join_links($this->Link(), $rssRelativeLink);
return $this->customise(array(
"RSSLink" => Text::create($rssLink),
));
}
}
Template:
:::php
<a href="$RSSLink.ATT">RSS feed</a>
Some rules of thumb:
- Don't concatenate URLs in a template. It only works in extremely simple cases that usually contain bugs.
- Use Controller::join_links() to concatenate URLs. It deals with query strings and other such edge cases.
Filtering incoming HTML from TinyMCE
In some cases you may be particularly concerned about which HTML elements are addable to Content via the CMS.
By default, although TinyMCE is configured to restrict some dangerous tags (such as script tags), this restriction
is not enforced server-side. A malicious user with write access to the CMS might create a specific request to avoid
these restrictions.
To enable server side filtering using the same whitelisting controls as TinyMCE, set the HtmlEditorField::$sanitise_server_side config property to true.
Cross-Site Request Forgery (CSRF)
SilverStripe has built-in countermeasures against CSRF identity theft for all form submissions. A form object
will automatically contain a SecurityID parameter which is generated as a secure hash on the server, connected to the
currently active session of the user. If this form is submitted without this parameter, or if the parameter doesn't
match the hash stored in the users session, the request is discarded.
You can disable this behaviour through [api:Form->disableSecurityToken()].
It is also recommended to limit form submissions to the intended HTTP verb (mostly GET or POST)
through [api:Form->setStrictFormMethodCheck()].
Sometimes you need to handle state-changing HTTP submissions which aren't handled through
SilverStripe's form system. In this case, you can also check the current HTTP request
for a valid token through [api:SecurityToken::checkRequest()].
Casting user input
When working with $_GET, $_POST or Director::urlParams variables, and you know your variable has to be of a
certain type, like an integer, then it's essential to cast it as one. Why? To be sure that any processing of your
given variable is done safely, with the assumption that it's an integer.
To cast the variable as an integer, place (int) or (integer) before the variable.
For example: a page with the URL paramaters mysite.com/home/add/1 requires that ''Director::urlParams['ID']'' be an
integer. We cast it by adding (int) - ''(int)Director::urlParams['ID']''. If a value other than an integer is
passed, such as mysite.com/home/add/dfsdfdsfd, then it returns 0.
Below is an example with different ways you would use this casting technique:
:::php
public function CaseStudies() {
// cast an ID from URL parameters e.g. (mysite.com/home/action/ID)
$anotherID = (int)Director::urlParam['ID'];
// perform a calculation, the prerequisite being $anotherID must be an integer
$calc = $anotherID + (5 - 2) / 2;
// cast the 'category' GET variable as an integer
$categoryID = (int)$_GET['category'];
// perform a byID(), which ensures the ID is an integer before querying
return CaseStudy::get()->byID($categoryID);
}
The same technique can be employed anywhere in your PHP code you know something must be of a certain type. A list of PHP cast types can be found here:
(int),(integer)- cast to integer(bool),(boolean)- cast to boolean(float),(double),(real)- cast to float(string)- cast to string(array)- cast to array(object)- cast to object
Note that there is also a 'SilverStripe' way of casting fields on a class, this is a different type of casting to the standard PHP way. See casting.
Filesystem
Don't allow script-execution in /assets
As all uploaded files are stored by default on the /assets-directory, you should disallow script-execution for this folder. This is just an additional security-measure to making sure you avoid directory-traversal, check for filesize and disallow certain filetypes.
Example configuration for Apache2:
<VirtualHost *:80>
...
<LocationMatch assets/>
php_flag engine off
Options -ExecCGI -Includes -Indexes
</LocationMatch>
</VirtualHost>
If you are using shared hosting or in a situation where you cannot alter your Vhost definitions, you can use a .htaccess file in the assets directory. This requires PHP to be loaded as an Apache module (not CGI or FastCGI).
/assets/.htaccess
php_flag engine off
Options -ExecCGI -Includes -Indexes
Don't allow access to .yml files
Yaml files are often used to store sensitive or semi-sensitive data for use by SilverStripe framework (for instance, configuration and test fixtures).
You should therefore block access to all yaml files (extension .yml) by default, and white list only yaml files you need to serve directly.
See Apache and Nginx installation documentation for details specific to your web server
User uploaded files
Certain file types are by default excluded from user upload. html, xhtml, htm, and xml files may have embedded, or contain links to, external resources or scripts that may hijack browser sessions and impersonate that user. Even if the uploader of this content may be a trusted user, there is no safeguard against these users being deceived by the content source.
Flash files (swf) are also prone to a variety of security vulnerabilities of their own, and thus by default are disabled from file upload. As a standard practice, any users wishing to allow flash upload to their sites should take the following precautions:
- Only allow flash uploads from trusted sources, preferably those with available source.
- Make use of the AllowScriptAccess parameter to ensure that any embedded Flash file is isolated from its environments scripts. In an ideal situation, all flash content would be served from another domain, and this value is set to "sameDomain". If this is not feasible, this should be set to "never". For trusted flash files you may set this to "sameDomain" without an isolated domain name, but do so at your own risk.
- Take note of any regional cookie legislation that may affect your users. See Cookie Law and Flash Cookies.
See the Adobe Flash security page for more information.
ADMIN privileged users may be allowed to override the above upload restrictions if the
File.apply_restrictions_to_admin config is set to false. By default this is true, which enforces these
restrictions globally.
Additionally, if certain file uploads should be made available to non-privileged users, you can add them to the
list of allowed extensions by adding these to the File.allowed_extensions config.
Passwords
SilverStripe stores passwords with a strong hashing algorithm (blowfish) by default (see [api:PasswordEncryptor]). It adds randomness to these hashes via salt values generated with the strongest entropy generators available on the platform (see [api:RandomGenerator]). This prevents brute force attacks with Rainbow tables.
Strong passwords are a crucial part of any system security. So in addition to storing the password in a secure fashion, you can also enforce specific password policies by configuring a [api:PasswordValidator]:
:::php
$validator = new PasswordValidator();
$validator->minLength(7);
$validator->checkHistoricalPasswords(6);
$validator->characterStrength(3, array("lowercase", "uppercase", "digits", "punctuation"));
Member::set_password_validator($validator);
In addition, you can tighten password security with the following configuration settings:
Member.password_expiry_days: Set the number of days that a password should be valid for.Member.lock_out_after_incorrect_logins: Number of incorrect logins after which the user is blocked from further attempts for the timespan defined in$lock_out_delay_minsMember.lock_out_delay_mins: Minutes of enforced lockout after incorrect password attempts. Only applies iflock_out_after_incorrect_loginsis greater than 0.Security.remember_username: Set to false to disable autocomplete on login form
Clickjacking: Prevent iframe Inclusion
"Clickjacking" is a malicious technique where a web user is tricked into clicking on hidden interface elements, which can lead to the attacker gaining access to user data or taking control of the website behaviour.
You can signal to browsers that the current response isn't allowed to be
included in HTML "frame" or "iframe" elements, and thereby prevent the most common
attack vector. This is done through a HTTP header, which is usually added in your
controller's init() method:
:::php
class MyController extends Controller {
public function init() {
parent::init();
$this->response->addHeader('X-Frame-Options', 'SAMEORIGIN');
}
}
This is a recommended option to secure any controller which displays or submits sensitive user input, and is enabled by default in all CMS controllers, as well as the login form.