Is addslashes() in PHP Truly Safe Against SQL Injection, Especially with Multibyte Characters?

PHP's addslashes() and SQL Injection: A Multibyte Character Vulnerability Analysis

While mysql_real_escape_string is the preferred method for securing user input in PHP SQL queries, understanding the limitations of addslashes() is vital. This function, under specific conditions, can leave your application susceptible to SQL injection attacks.

The addslashes() Weakness

The primary weakness of addslashes() stems from its inadequate handling of multibyte characters. When a single or double quote resides within a multibyte character sequence, addslashes() prefaces the quote with a backslash. However, if this backslash becomes integrated into a valid multibyte character, its escaping function is compromised.

This allows an attacker to construct malicious input containing a multibyte character incorporating a backslash followed by a quote. This cleverly bypasses the intended escaping mechanism, enabling the quote to function as the initiation point of an SQL injection command.

Effective Mitigation Strategies

To effectively prevent this vulnerability, completely avoid using addslashes() for sanitizing user input destined for SQL queries. Instead, consistently employ mysql_real_escape_string (or its prepared statement equivalents for even better security), which is specifically designed to manage multibyte characters and effectively neutralize SQL injection threats.

Key Takeaway

addslashes() is a deprecated function for input sanitization. Recognizing its vulnerabilities is essential for building secure PHP applications. By adopting safer alternatives like mysql_real_escape_string and, ideally, prepared statements, developers can significantly reduce the risk of successful SQL injection attacks.

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