Is mysql_real_escape_string Sufficient to Prevent SQL Injection?

mysql_real_escape_string: Limitations and Usage

Introduction

While mysql_real_escape_string is often used to protect against SQL injection, it has certain limitations that can leave applications vulnerable.

Correct Usage and Limitations

mysql_real_escape_string is intended for escaping text content used as a value within quotes in an SQL statement. Incorrectly applying it, such as in unquoted values or entire SQL statements, can lead to injection risks.

Invalid or Unescapable Values

Numeric values and unquoted input cannot be effectively escaped using mysql_real_escape_string. For numeric values, casting to the appropriate type is recommended, while unquoted input should be handled as strings within the query.

Example of Incorrect Usage

mysql_query('DELETE FROM users WHERE user_id = '.mysql_real_escape_string($input));

This example does not protect against SQL injection if the input includes "5 OR 1=1". It treats the input as a numeric value when escaping, even though the query expects a string. Proper handling involves wrapping the escaped input in quotes.

Subtle Vulnerabilities

Another potential issue arises when using mysql_query("SET NAMES 'utf8'", $link) to set the database connection encoding rather than mysql_set_charset('utf8', $link). This creates a mismatch between the client API's assumed encoding and the database's interpretation, potentially leading to injection vulnerabilities with multibyte strings.

Conclusion

mysql_real_escape_string has fundamental limitations, particularly in ensuring correct usage. It is crucial to understand its intended purpose and avoid applying it incorrectly. Consider using alternative and more secure methods such as prepared statements for improved protection against SQL injection.

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