PHP prevents SQL injection with built-in function analysis

SQLInjection attack is the most common method used by hackers to attack websites. If your site does not use strict user input validation, it is often vulnerable to SQLinjection attacks. SQL injection attacks are usually implemented by submitting bad data or query statements to the site database, which may cause records in the database to be exposed, changed or deleted. In order to prevent SQL

injection attacks

, PHP comes with a function that can process the input string and perform preliminary security processing on the input at the lower level, that is, Magic Quotes. (php.ini magic_quotes_gpc). If the magic_quotes_gpc option is enabled, single quotes, double quotes, and other characters in the input string will be automatically preceded by a backslash /. But Magic Quotes is not a very universal solution, it does not block all potentially dangerous characters, and Magic Quotes is not enabled on many servers. Therefore, we also need to use various other methods to prevent

sql injection

. Many databases provide this input data processing functionality natively. For example, PHP's MySQL operation functions include addslashes(), mysql_real_escape_string(), mysql_escape_string() and other functions, which can escape

special characters

and characters that may cause database operation errors. So what are the differences between these three functional functions? Let’s talk about it in detail below. Although many

PHP programmers

in China still rely on addslashes to prevent sql injection, it is still recommended that everyone strengthen checks to prevent sql injection in Chinese. The problem with addslashes is that hackers can use 0xbf27 instead of single quotes, while addslashes only changes 0xbf27 to 0xbf5c27, which becomes a valid multi-byte character. 0xbf5c is still regarded as a single quote, so addslashes cannot successfully intercept. Of course, addslashes is not useless. It is used for processing single-byte strings. For multi-byte characters, use mysql_real_escape_string.

In addition, for the example of get_magic_quotes_gpc in the PHP manual:

<code><span>if</span> (!get_magic_quotes_gpc()) {
    <span>$lastname</span> = addslashes(<span>$_POST</span>[‘lastname’]);
} <span>else</span> {
    <span>$lastname</span> = <span>$_POST</span>[‘lastname’];
}</code>

It is best to check $_POST[’lastname’] when magic_quotes_gpc is already open.

Let’s talk about the difference between the two functions mysql_real_escape_string and mysql_escape_string:

mysql_real_escape_string can only be used under (PHP 4 >= 4.3.0, PHP 5). Otherwise, you can only use mysql_escape_string. The difference between the two is: mysql_real_escape_string takes into account the current character set of the connection, while mysql_escape_string does not.

To summarize:

addslashes() forcibly adds /;

• mysql_real_escape_string() will determine the character set, but there are requirements for the PHP version;
• mysql_escape_string does not consider the current character set of the connection.
• To prevent

sql injection

in dz is to use the addslashes function, and at the same time make some replacements in the dthmlspecialchars function $string = preg_replace('/&(((#(/d{3,5}|x[a -fA-F0-9]{4}));)/', '&//1', this replacement solves the injection problem and also solves some problems with Chinese garbled characters

http://blog. .csdn.net/hellollx/article/details/5399760

The above has introduced the analysis of PHP's own functions to prevent SQL injection, including the relevant aspects. I hope it will be helpful to friends who are interested in PHP tutorials.