Yii Framework Official Guide Series 51 - Special Topic: Security Measures (Security)

1. Prevention of cross-site scripting attacks

Cross-site scripting attacks (referred to as XSS), that is, web applications collect information from users User data. Attackers often inject JavaScript, VBScript, ActiveX, HTML or Flash into vulnerable web applications to confuse visitors and collect visitor information. For example, a poorly designed forum system may display user input without checking. An attacker can inject a piece of malicious JavaScript code into the post content. In this way, when other visitors read this post, these JavaScript codes can be run on the visitor's computer.

One of the most important measures to prevent XSS attacks is: Content inspection before displaying the content entered by the user. For example, you can escape HTML in content. But in some cases this method is not advisable, because this method disables all HTML tags.

Yii integrates HTMLPurifier and provides developers with a very useful component CHtmlPurifier, which encapsulates the HTMLPurifier class. It can remove all malicious code from the audited content through effective review, security and whitelisting functions, and ensure that the content filtered after filtering meets standards.

CHtmlPurifier component can be used as a widget or filter. When used as a widget, CHtmlPurifier can safely filter the content displayed in the view. The following is a code example:

##

3985325355f9adb62c26998b2d6e1066beginWidget('CHtmlPurifier'); ?>
//...这里显示用户输入的内容...
3985325355f9adb62c26998b2d6e1066endWidget(); ?>

2. Prevention of cross-site request forgery attacks

Cross-site request forgery (referred to as CSRF) attack, that is, when the user's browser visits a malicious website, the attacker causes the user's browser to initiate an attacker-specified request to a trusted website. For example, a malicious website has an image, and the

src address of this image points to a bank website: //m.sbmmt.com/. If the user visits this malicious webpage after logging into the bank's website, the user's browser will send an instruction to the bank's website. The content of this instruction may be "transfer 10,000 yuan to the attacker's account." Cross-site attacks take advantage of a specific website that the user trusts, while CSRF attacks, on the contrary, take advantage of the user's specific user identity on a website.

To prevent CSRF attacks, you must remember one thing:

GET The request only allows retrieval of data and cannot modify any data on the server. The POST request should contain some random values ​​that can be recognized by the server to ensure that the source of the form data and the destination of the running results are the same.

Yii implements a CSRF prevention mechanism to help prevent attacks based on

POST. The core of this mechanism is to set a random data in the cookie, and then compare it with the corresponding value in the POST data submitted by the form.

By default, CSRF prevention is disabled. If you want to enable it, you can edit the CHttpRequest section of the component in the application configuration.

Code example:

return array(
    'components'=>array(
        'request'=>array(
            'enableCsrfValidation'=>true,
        ),
    ),
);

To display a form, use CHtml::form instead of writing HTML code yourself. Because CHtml::form can automatically embed a hidden item in the form. This hidden item stores random data required for verification. This data can be sent to the server for verification when the form is submitted.

3. Prevention of Cookie Attacks

It is very important to protect cookies from attacks. Because session ID is usually stored in Cookie. If the attacker steals a valid session ID, he can use the session information corresponding to this session ID.

Here are a few precautions:

• You can use SSL to create a secure channel and only send the authentication cookie over an HTTPS connection. In this way, the attacker cannot decrypt the cookie sent.

• Set the expiration time of cookies. Do the same for all cookies and seesion tokens. This reduces the chance of being attacked.

• Prevent cross-site code attacks, because it can trigger arbitrary code in the user's browser, and these codes may leak the user's cookies.

• Verify the cookie content when the cookie changes.

Yii implements a cookie verification mechanism to prevent cookies from being modified. After enabling, HMAC checking of cookie values ​​can be performed.

Cookie verification is disabled by default. If you want to enable it, you can edit the CHttpRequest section of the component in the application configuration.

Code example:

return array(
    'components'=>array(
        'request'=>array(
            'enableCookieValidation'=>true,
        ),
    ),
);

Be sure to use Yii verified cookie data. Use Yii's built-in cookies component to perform cookie operations. Do not use

$_COOKIES.

// 检索一个名为$name的cookie值
$cookie=Yii::app()->request->cookies[$name];
$value=$cookie->value;
......
// 设置一个cookie
$cookie=new CHttpCookie($name,$value);
Yii::app()->request->cookies[$name]=$cookie;

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