"2022" is a must know web security interview question for job hopping

Hi, I'm from the front , Today, I would like to share with you ！ I don't say much nonsense , Direct delivery of dry goods ！

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1、 You are right about WEB The understanding of safety ？

The Internet is developing rapidly , current web It is no longer a simple web page , In addition to the common e-commerce shopping platform 、 Mobile transfer 、 Outside the banking system , The development of Internet of things technology , Not only let smart home into life , It also promotes medical 、 The development of logistics and other industries , Security has gradually become a matter of concern .

As a front-end programmer, I am most concerned about web It's safe , The more common and harmful ones are XSS Cross site scripts gongji、SQL Inject 、CSFR Cross Site Request Forgery, etc gongji The way . We need to better understand their malice gongji principle , In order to better defense gongji.

2、XSS Cross site scripts gongji

XSS yes Cross Site Scripting Abbreviation , In order to CSS Make a distinction , So it's called XSS .

XSS gongji Mainly web The page is implanted with malicious script Code , When a user visits a page , Embedded malicious code automatically executes , So as to achieve gongji The effect of .XSS There are three types ：

• reflective XSS
• Storage type XSS
• Document type XSS

reflective XSS When making a network request , malice gongji The code appears in url in , Submit as input to the server , The server returns to the browser , Browser execution XSS Code , This process is like a reflection , So it's called reflective XSS gongji.

Log in and copy

      
      

       
       http://www.xxx.com?q=<script>alert(" Malicious script ")</script>
       
       
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http://www.xxx.com?n=<img sec="1 onerror=alert(' Malicious code ')">
      
      
      
      

       
       
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Storage type XSS It's submitted XSS The code is stored in the server's database 、 In memory or file system , Don't submit again the next time you request the target page XSS Code . Common in user input .

Document type XSS It doesn't go through the server , As a middleman , Hijacking network packets during data transmission , Then modify the html file .

XSS More harm , It is common to steal accounts 、 Steal business value information, etc . So we need to take some defensive measures to protect the rights and interests of users , For the above three gongji The way , There are three corresponding defensive measures , Respectively ：

• Escape coding between client and server

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       <script>alert(' Malicious code ')</script>
      
      
      
      

       
       
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After escaping the code, the editor will reprocess it for you , Students who don't know can try it by themselves ！

• Filter out dangerous nodes , Such as script、style、link、iframe .
• utilize CSP

Content Security Policy Content security policy , You can specify the whitelist of resources that can be loaded on the current web page , So as to reduce the impact of web pages XSS gongji The risk of .

3、CSRF How to defend, you know ？

CSFR yes cross site request forgery , The Chinese name is cross site request forgery . Also known as ：one click attack/session riding, Abbreviation for ：CSRF / XSRF.

CSRF Mainly gongji The identity of the user is stolen , Malicious operation in the name of the user , It is easy to cause personal privacy disclosure and property security problems , therefore CSRF Our defense measures cannot be less , You can start from both server and client , Its defense methods are as follows ：

• Check http The head of the referer Information
• Use a one-time token
•   Key operations use POST request
• Use verification code

The specific defensive measures are ：

1>、 Check http The head of the referer Information

referer Included in http Request header , Indicates the page source of the request interface , The server passes the check referer Information , Intercept the request when it is found that it comes from a foreign domain , Block unknown requests , To some extent, it can reduce gongji.

2>、 Use a one-time token

Use a one-time token for identification ,heike You cannot get a one-time token across domains , Therefore, the server can judge whether to carry a one-time token , Some illegal operators can be excluded .

3>、 Key operations use POST request

Sensitive operations use POST request , It is mainly to prevent user sensitive information from appearing in url in , Easy to reveal important information .

4>、 Use verification code

CSRF gongji Basically, it occurs when users don't know , Secretly send network requests when users are not aware , If verification code is used , It needs to be verified every time important operations are carried out , Thus, the defense is simple and effective CSRF gongji.

4、SQL What is injection ？

So-called SQL To inject is to put SQL Insert the statement command into web Query string for form submission or page request , Finally, the malicious execution of the server is achieved SQL command . It is a common WEB Security loudong,gongji People will take advantage of this loudong, You can access or modify data , Leverage potential databases loudong Conduct gongji.

SQL Injection can be divided into the following examples ：

• Digital injection
• Character injection
• Other types

SQL Precautions against injection ：

• Add regular validation and filtering . Where the user enters , Don't trust user input , Regular expression validation is required for user input .
• Sensitive fields should be encrypted . Confidential and sensitive information cannot be stored directly , Need encryption or hash Drop sensitive information .
• Do not use administrator privileges to connect to the database . Use separate permissions for each application to control limited database connections , Never connect to a database with administrator privileges .
• Dynamic splicing is not allowed SQL sentence . You can use parameterized SQL Or directly use stored procedures for data query access , But don't dynamically splice .

5、DDOS

DDOS yes Distributed Denial of Service Abbreviation , Distributed denial of service .DDOS gongji It refers to the use of customers / Server technology , Combine multiple computers as gongji platform , Launch on one or more targets DDOS gongji, So as to double the denial of service gongji The power of . The gongji The method mainly uses the defect of the network service function of the target system or directly consumes its system resources , Make the target system unable to provide normal services .

DDOS gongji Use a lot of resources through a large number of legitimate requests , In order to achieve the purpose of paralyzing the network , There are several specific forms of expression ：

1. By overloading the network to interfere with or even block the normal network communication ;
2. By submitting a large number of requests to the server , Overload the server ;
3. Block a user from accessing the server ;
4. Block the communication between a service and a specific system or individual .

6、DNS hijacked

DNS It is to map the network domain name to the one that can be recognized by the real computer IP Address , For further communication .DNS Hijacking is when a user visits a site through a domain name , Tampered with DNS The server returns the of a phishing website IP, Users are hijacked to phishing sites , And reveal privacy .

7、HTTP hijacked

HTTP Hijacking is when a user visits a website , Will pass through the operator , Operators can intercept the content requested to be returned by colluding with black factories , And tamper with the returned content and then return it to the user . Generally, some advertisements will be inserted after the website is hijacked , Seriously, it may be directly modified into phishing websites to steal user information .

Defensive measures ：

The identity of the other party and data integrity are not verified in the communication process , So prevent HTTP The only way to hijack is to encrypt the content , So that the hijacker cannot pojie Tampering , This will prevent HTTP Hijacked .