Magic quotes was a feature of the PHP scripting language, wherein strings are automatically escaped—special characters are prefixed with a backslash—before being passed on. It was introduced to help newcomers write functioning SQL commands without requiring manual escaping. It was later described as intended to prevent inexperienced developers from writing code that was vulnerable to SQL injection attacks.
This feature was officially deprecated as of PHP 5.3.0 and removed in PHP 5.4, due to security concerns.
The current revision of the PHP manual mentions that the rationale behind magic quotes was to "help [prevent] code written by beginners from being dangerous." It was however originally introduced in PHP 2 as a php.h compile-time setting for msql, only escaping single quotes, "making it easier to pass form data directly to msql queries". It originally was intended as a "convenience feature, not as [a] security feature."
The use scope for magic quotes was expanded in PHP 3. Single quotes, double quotes, backslashes and null characters in all user-supplied data all have a backslash prepended to them before being passed to the script in the
$_COOKIE global variables. Developers can then in theory use string concatenation to construct safe SQL queries with data provided by the user. (This was most accurate when PHP 2 and PHP 3 were current, since the primary supported databases allowed only 1-byte character sets.)
Magic quotes were enabled by default in new installations of PHP 3 and 4, but could be disabled through the
magic_quotes_gpc configuration directive. Since the operation of magic quotes was behind the scenes and not immediately obvious, developers may have been unaware of their existence and the potential problems that they could introduce. The PHP documentation pointed out several pitfalls and recommended that, despite being enabled by default, they should be disabled.
Problems with magic quotes included:
addslashes()function, which is not Unicode-aware and is still subject to SQL injection vulnerabilities in some multi-byte character encodings. Database-specific functions such as
mysql_real_escape_string()or, where possible, prepared queries with bound parameters, are preferred.
In November 2005 the core PHP developers decided that because of these problems, the magic quotes feature would be removed from PHP 6. When development of PHP 6 stalled and development continued on the 5.x branch instead, the feature was deprecated in PHP 5.3.0 and removed in 5.4.
Edited: 2021-06-18 14:11:23