How to bypass single quote escaping in ThinkPHP

ThinkPHP is a popular PHP framework. We often need to operate on data in the database during the development process, and SQL injection is a common security threat. To prevent SQL injection attacks, we need to escape special characters. When using the framework's own data manipulation functions, the framework has already escaped special characters, but when using native SQL, you need to handle the escaping yourself. This article will introduce how to bypass single quote escaping in ThinkPHP.

When using native SQL, we usually use PDO prepared statements to prevent SQL injection attacks, for example:

$sql = 'SELECT * FROM users WHERE username = :username';
$sth = $dbh->prepare($sql);
$sth->bindParam(':username', $username);
$sth->execute();

This method can effectively avoid SQL injection attacks, because PDO will automatically Escape special characters and also improve query performance.

However, in some cases we need to use native SQL, which requires us to handle SQL escaping ourselves. For example:

$username = $_GET['username'];
$sql = "SELECT * FROM users WHERE username = '".addslashes($username)."'";

This method is a common way to handle SQL escape. Special characters are escaped through the addslashes function. However, this approach is not secure because in many cases, SQL injection attacks can be performed by bypassing the addslashes function. Suppose we use single quotes to wrap special characters, for example:

$username = "123' OR '1'='1";
$sql = "SELECT * FROM users WHERE username = '".addslashes($username)."'";

The query result of this SQL statement will return all user information, because at this time the logic of the SQL statement becomes:

SELECT * FROM users WHERE username = '123' OR '1'='1'

Since '1'='1' is always true, the query result of this SQL statement is all user information. This is how SQL injection works. However, we can use some methods to bypass single quote escaping, so that even if ' is used for injection attacks, it will not cause any harm.

The method to bypass single quote escaping is as follows:

1. Use double quotes

Double quotes are a legal character in SQL, so we Double quotes can be used to bypass single quote escaping. For example:

$username = '123" OR "1"="1';
$sql = 'SELECT * FROM users WHERE username = "'.$username.'"';

The query result of this SQL statement will return all user information, because the logic of the SQL statement becomes:

SELECT * FROM users WHERE username = '123" OR "1"="1'

At this time, the content in double quotes Will be executed as a whole and will not be affected by single quote escaping. Therefore, using double quotes can effectively bypass single quote escaping. However, it should be noted that using double quotes may encounter escaping problems. For example, double quotes themselves need to be escaped using '\'.

2. Use backslash

Backslash '\' is the escape character in SQL. Use backslash in SQL to escape special characters. , for example:

$username = '123\' OR \'1\'=\'1';
$sql = 'SELECT * FROM users WHERE username = "'.$username.'"';

At this time, the logic of the escaped SQL statement becomes:

SELECT * FROM users WHERE username = '123' OR '1'='1'

Because '\' can be recognized normally in the SQL syntax, use '\' It is possible to escape. However, it should be noted that since '\' itself is also an escape character in PHP, you need to use the double escape character '\\'' to represent '\' in PHP.

3. Use the CHR function

The CHR function can convert integers into corresponding ASCII code characters. We can use the CHR function to convert single quotes into ASCII codes, thereby bypassing Escape through single quotes, for example:

$username = '123'.chr(39).' OR 1=1';
$sql = 'SELECT * FROM users WHERE username = "'.$username.'"';

At this time, the logic of the escaped SQL statement becomes:

SELECT * FROM users WHERE username = '123' OR 1=1

Because chr(39) can get the ASCII code of single quotes, Therefore, using the CHR function can also effectively bypass single quote escaping.

Bypassing single quote escaping is a common technique in SQL injection attacks. To defend against such attacks, you need to pay attention to escaping special characters when using native SQL. At the same time, you need to pay attention to using way of escaping. When using the framework's own data manipulation functions, the risk of SQL injection attacks can be effectively reduced.

The above is the detailed content of How to bypass single quote escaping in ThinkPHP. For more information, please follow other related articles on the PHP Chinese website!