Summary of some methods to prevent SQL injection attacks (1/2)

Summary of some methods to prevent SQL injection attacks (1/2)_PHP tutorial

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Release： 2016-07-13 10:47:53

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Here the editor will share with you some examples and experiences of preventing SQL injection attacks summarized by webmasters. I hope this tutorial can provide some help to all students.

1. Configuration on the server side

Security, PHP code writing is one aspect, and PHP configuration is very critical.

We installed PHP manually. The default configuration file of PHP is in /usr/local/apache2/conf/php.ini. Our most important thing is to configure the content in php.ini so that we can execute PHP more safely. The security settings in the entire PHP are mainly to prevent attacks from phpshell and SQL Injection. Let’s discuss it slowly. We first use any editing tool to open /etc/local/apache2/conf/php.ini. If you install it in other ways, the configuration file may not be in this directory.

(1) Turn on the safe mode of php

php’s safe mode is a very important built-in security mechanism that can control some functions in php, such as system(),

At the same time, the permissions of many file operation functions are controlled, and certain key files, such as /etc/passwd, are not allowed.

But the default php.ini does not open safe mode, let’s open it:

safe_mode = on

(2) User group security

When safe_mode is turned on, safe_mode_gid is turned off, then the php script can access the file, and it is the same

Users in the

group can also access the file.

Recommended settings are:

safe_mode_gid = off

If we don’t set it up, we may not be able to operate the files in our server website directory. For example, we need to

When operating on files.

(3) The main directory of the execution program in safe mode

If safe mode is turned on but you want to execute certain programs, you can specify the home directory of the program to be executed:

safe_mode_exec_dir = D:/usr/bin

Generally, there is no need to execute any program, so it is recommended not to execute the system program directory. You can point to a directory,

Then copy the program that needs to be executed, such as:

safe_mode_exec_dir = D:/tmp/cmd

However, I recommend not to execute any program, then you can point to our web directory:

safe_mode_exec_dir = D:/usr/www

(4) Include files in safe mode

If you want to include certain public files in safe mode, then change the options:

safe_mode_include_dir = D:/usr/www/include/

In fact, generally the files included in php scripts have been written in the program itself. This can be set according to specific needs.

(5) Control the directories that php scripts can access

Use the open_basedir option to control the PHP script to only access the specified directory, which can prevent the PHP script from accessing

Files that should not be accessed limit the harm of phpshell to a certain extent. We can generally set it to only access the website directory:

open_basedir = D:/usr/www

(6) Turn off dangerous functions

If safe mode is turned on, function prohibition is not necessary, but we still consider it for safety. For example,

We don’t think we want to execute php functions including system() that can execute commands, or that can view php information

phpinfo() and other functions, then we can ban them:

disable_functions = system,passthru,exec,shell_exec,popen,phpinfo

If you want to prohibit any file and directory operations, you can close many file operations

disable_functions = chdir,chroot,dir,getcwd,opendir,readdir,scandir,fopen,unlink,delete,copy,mkdir, rmdir,rename,file,file_get_contents,fputs,fwrite,chgrp,chmod,chown

The above only lists some of the commonly used file processing functions. You can also combine the above execution command function with this function,

It can resist most phpshells.

(7) Close the leakage of PHP version information in the http header

In order to prevent hackers from obtaining the PHP version information in the server, we can turn off the information in the http header:

expose_php = Off

For example, when a hacker telnet www.12345.com 80, he will not be able to see PHP information.

(8) Close registration of global variables

Variables submitted in PHP, including those submitted using POST or GET, will be automatically registered as global variables and can be accessed directly,

This is very unsafe for the server, so we can’t let it be registered as a global variable, so we turn off the register global variable option:

register_globals = Off

Of course, if this is set, then reasonable methods must be used to obtain the corresponding variables, such as obtaining the variable var submitted by GET,

Then you need to use $_GET['var'] to get it. PHP programmers should pay attention to this.

(9) Turn on magic_quotes_gpc to prevent SQL injection

SQL injection is a very dangerous problem. In the smallest case, the website backend may be invaded, or in the worst case, the entire server may collapse.

So be careful. There is a setting in php.ini:

magic_quotes_gpc = Off

This is turned off by default. If it is turned on, it will automatically convert the SQL query submitted by the user,

For example, convert ' to ', etc., which plays a significant role in preventing sql injection. So we recommend setting it to:

magic_quotes_gpc = On

(10) Error message control

Generally, PHP will prompt an error when it is not connected to the database or under other circumstances. Generally, the error message will contain a PHP script when

The path information before

or the query SQL statement and other information are unsafe if provided to hackers, so it is generally recommended that servers disable error prompts:

display_errors = Off

If you want to display an error message, be sure to set the level of display error, for example, only display information above warning:

error_reporting = E_WARNING & E_ERROR

Of course, I still recommend turning off error prompts.

(11) Error log

It is recommended to record the error information after turning off display_errors, so as to find the reason why the server is running:

log_errors = On

At the same time, you must also set the directory where the error log is stored. It is recommended that the root apache log be stored together:

error_log = D:/usr/local/apache2/logs/php_error.log

Note: The file must be given to allow the apache user and group to have write permissions.

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