What are the potential pitfalls of using incorrect regular expression syntax in PHP for password validation?

Using incorrect regular expression syntax for password validation in PHP can lead to security vulnerabilities or incorrect validation of passwords. It's important to use the correct regular expression syntax to ensure that passwords meet the desired criteria, such as minimum length, uppercase letters, lowercase letters, numbers, and special characters. 

// Correct regular expression syntax for password validation
$password = "MySecurePassword123!";

if (preg_match('/^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[@$!%*?&])[A-Za-z\d@$!%*?&]{8,}$/', $password)) {
    echo "Password is valid.";
} else {
    echo "Password is invalid.";
}

Keywords

Regular expression syntax error password validation PHP pitfalls

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