PHP + SQL injection technology implementation and Prevention Measures

Recently, PHP + MYSQL programming has been involved. I learned a little about PHPSQL injection attacks and summarized my experience. In my opinion, the main cause of SQL injection attacks is the following two reasons:

Recently, PHP + MYSQL programming has been involved. I learned some knowledge about php SQL injection attacks and summarized my experience. In my opinion, the main cause of SQL injection attacks is the following two reasons:

1. The magic_quotes_gpc option in the php configuration file php. ini is disabled.
2. The developer does not check and escape the data type.
But in fact, the second point is the most important. In my opinion, it should be the most basic quality for web programmers to check the data types entered by users and submit the correct data types to MYSQL. But in reality, many small Web developers often forget this, leading to a wide open backdoor.
Why is the second most important? Without the second guarantee, the magic_quotes_gpc option may cause SQL injection attacks, whether on or off. The following describes the technical implementation:
1. injection attack when magic_quotes_gpc = Off
Magic_quotes_gpc = Off is a very insecure option in php. The new php version has changed the default value to On. However, there are still a considerable number of server options that are off. After all, some old servers are also used.
When magic_quotes_gpc = On, it will include all '(single quotes), "(double signs), \ (backslash), and white space characters in the submitted variables, \ is automatically added to the front \. The official instructions for php are as follows:

The Code is as follows:

Magic_quotes_gpc boolean
Sets the magic_quotes state for GPC (Get/Post/Cookie) operations. when magic_quotes are on, all' (single-quote), "(double quote), \ (backslash) and NUL's are escaped with a backslash automatically

If there is no escape, that is, off, attackers can take advantage of it. The following test script is used as an example:

The Code is as follows:

If (isset ($ _ POST ["f_login"])
{
// Connect to the database...
//... Code omitted...

// Check whether the user exists
$ T_strUname = $ _ POST ["f_uname"];
$ T_strPwd = $ _ POST ["f_pwd"];
$ T_strSQL = "SELECT * FROM tbl_users WHERE username = '$ t_strUname' AND password = '$ t_strPwd' LIMIT ";

If ($ t_hRes = mysql_query ($ t_strSQL ))
{
// Processing after successful query...
}
}
?>
Sample test

In this script, when the user enters the normal user name and password, assuming the values are zhang3 and abc123, the SQL statement submitted is as follows:

The Code is as follows:

SELECT * FROM tbl_users
WHERE username = 'hangzhou3' AND password = 'abc123' LIMIT

If the attacker enters zhang3 'OR 1 = 1 # In the username field and abc123 in the password field, the SQL statement submitted is changed to the following:

The Code is as follows:

SELECT * FROM tbl_users
WHERE username = 'hangzhou' OR 1 = 1 # 'AND password = 'abc123' LIMIT

Because # Is a comment character in mysql, # the subsequent statement is not executed, and the above statement is implemented:

The Code is as follows:

SELECT * FROM tbl_users
WHERE username = 'hangzhou3' OR 1 = 1

In this way, attackers can bypass authentication. If attackers know the database structure, it is more dangerous to construct a union select statement:
Assume that in username, enter: zhang3 'OR 1 = 1 UNION select cola, colb, cold FROM tbl_ B #
Enter abc123 in password,
The submitted SQL statement is changed:

The Code is as follows:

SELECT * FROM tbl_users
WHERE username = 'hangzhou3'
OR 1 = 1 UNION select cola, colb, cold FROM tbl_ B # 'AND password = 'abc123' LIMIT 0, 1

This is quite dangerous. If the agic_quotes_gpc option is on and the quotation marks are escaped, the attack statement constructed by the above attacker will become like this and thus cannot achieve its purpose:

The Code is as follows:

SELECT * FROM tbl_users
WHERE username = 'hangzhou3 \ 'OR 1 = 1 #'
AND password = 'abc123'
LIMIT 0, 1
SELECT * FROM tbl_users
WHERE username = 'zhang3 \ 'OR 1 = 1 UNION select cola, colb, cold FROM tbl_ B #'
AND password = 'abc123' LIMIT 0, 1

2. injection attack when magic_quotes_gpc = On
When magic_quotes_gpc = On, attackers cannot perform SQL Injection On fields of the stable type. This does not mean this is safe. In this case, you can use numeric fields for SQL injection.
In MYSQL 5.x of the latest version, data type input is strictly specified, and automatic type conversion is disabled by default. A numeric field cannot be a quote type marked with quotation marks. That is to say, if the uid is numeric, in the previous mysql version, such a statement is legal:

The Code is as follows:

Insert into tbl_user SET uid = "1 ";
SELECT * FROM tbl_user WHERE uid = "1 ";

In the latest MYSQL 5.x, the preceding statement is not legal and must be written as follows:

The Code is as follows:

Insert into tbl_user SET uid = 1;
SELECT * FROM tbl_user WHERE uid = 1;

In this case, I think it is correct. As a developer, it is the most basic requirement to submit correct data types that comply with the Rules to the database.
How can attackers attack magic_quotes_gpc = On? It is very simple, that is, SQL injection to numeric fields. The following php script is used as an example:

The Code is as follows:

If (isset ($ _ POST ["f_login"])
{
// Connect to the database...
//... Code omitted...
// Check whether the user exists
$ T_strUid = $ _ POST ["f_uid"];
$ T_strPwd = $ _ POST ["f_pwd"];
$ T_strSQL = "SELECT * FROM tbl_users WHERE uid = $ t_strUid AND password = '$ t_strPwd' LIMIT 0, 1 ";
If ($ t_hRes = mysql_query ($ t_strSQL ))
{
// Processing after successful query...
}
}
?>
Sample test

The above script requires the user to enter userid and password to log on. A normal statement. The user inputs 1001 and abc123. The SQL statement submitted is as follows:
SELECT * FROM tbl_users WHERE userid = 1001 AND password = 'abc123' LIMIT
If the attacker inputs 1001 OR 1 = 1 # At userid, the SQL statement injected is as follows:
SELECT * FROM tbl_users WHERE userid = 1001 OR 1 = 1 # AND password = 'abc123' LIMIT
The attacker achieved the goal.
Iii. How to Prevent php SQL injection attacks
How to Prevent php SQL injection attacks? In my opinion, the most important thing is to check and escape data types. The following rules are summarized:
The display_errors option in php. ini should be set to display_errors = off. In this way, php scripts do not output errors on web pages, so that attackers can analyze the information.
When calling mysql functions such as mysql_query, add @, I .e. @ mysql_query (...), so that mysql errors will not be output. Similarly, attackers may not analyze useful information. In addition, some programmers are used to output errors and SQL statements when mysql_query errors during development, such:

The Code is as follows: