Security improvements to PHP functions in different PHP versions

PHP version update brings function security improvements: the strcmp() function fixes the buffer overflow vulnerability and uses strict comparison operators. The json_decode() function disables PHP code execution by default to prevent arbitrary code injection. The crypt() function upgrades the hash algorithm to BCrypt to enhance password security. The mysqli extension introduces a new prepared statement API that provides better SQL injection protection.

PHP function security improvements between versions

As a popular web development language, PHP has been constantly updated to improve security. With each version iteration, the PHP team has made improvements to many commonly used functions to enhance application security. This article will explore the security improvements of PHP functions in different PHP versions and provide practical cases.

strcmp function

Prior to PHP 5.3, the strcmp() function was vulnerable to buffer overflow attacks. In PHP 5.3 and higher, this function was rewritten to prevent this type of attack.

Practical case:

// PHP 5.2 中容易受到攻击
$input = $_GET['input'];
if (strcmp($input, 'sensitive_data') == 0) {
    // 触发敏感操作
}

// PHP 5.3 及更高版本
$input = $_GET['input'];
if (strcmp($input, 'sensitive_data') === 0) {
    // 安全地比较字符串
}

json_decode function

Before PHP 5.4, json_decode() function Allows arbitrary PHP code to exist in user-supplied JSON data. In PHP 5.4 and above, this function disables PHP code execution by default.

Practical case:

// PHP 5.3 及更低版本容易受到攻击
$json = '{"code": "print_r($_POST);"}';
$obj = json_decode($json);

// 触发 PHP 代码执行（已禁用）
if (isset($obj->code)) {
    eval($obj->code);
}

crypt function

Before PHP 5.5, crypt() The function uses the weak hash algorithm MD5. In PHP 5.5 and above, this function defaults to BCrypt, a more secure password hashing algorithm.

Practical case:

// PHP 5.4 及更低版本使用 MD5
$password = 'my_password';
$hashed_password = crypt($password);

// PHP 5.5 及更高版本使用 BCrypt
$password = 'my_strong_password';
$hashed_password = crypt($password);

mysqli extension

Before PHP 7.1, mysqli extension was processed Vulnerable to SQL injection attacks when preparing statements. In PHP 7.1 and higher, this extension introduces the new prepared statement API, which provides better protection.

Practical case:

// PHP 7.0 及更低版本容易受到攻击
$stmt = $mysqli->prepare("SELECT * FROM users WHERE username = ?");
$stmt->bind_param("s", $username);

// PHP 7.1 及更高版本
$stmt = $mysqli->prepare("SELECT * FROM users WHERE username = ?");
$stmt->bind_param("s", $username, 1);

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