01. Keep software up to date
It may seem obvious, but ensuring you keep all software up to date is vital in keeping your site secure. This applies to both the server operating system and any software you may be running on your website such as a CMS or forum. When website security holes are found in software, hackers are quick to attempt to abuse them.
If you are using a managed hosting solution then you don’t need to worry so much about applying security updates for the operating system as the hosting company should take care of this.
If you are using third-party software on your website such as a CMS or forum, you should ensure you are quick to apply any security patches. Most vendors have a mailing list or RSS feed detailing any website security issues. WordPress, Umbraco and many other CMSes notify you of available system updates when you log in.
02. SQL injection
SQL injection attacks are when an attacker uses a web form field or URL parameter to gain access to or manipulate your database. When you use standard Transact SQL it is easy to unknowingly insert rogue code into your query that could be used to change tables, get information and delete data. You can easily prevent this by always using parameterised queries, most web languages have this feature and it is easy to implement.
Consider this query:
"SELECT * FROM table WHERE column = '" + parameter + "';"
If an attacker changed the URL parameter to pass in ‘ or ‘1’=’1 this will cause the query to look like this:
"SELECT * FROM table WHERE column = '' OR '1'='1';"
Since ‘1’ is equal to ‘1’ this will allow the attacker to add an additional query to the end of the SQL statement which will also be executed.
04. Error messages
Be careful with how much information you give away in your error messages. For example if you have a login form on your website you should think about the language you use to communicate failure when attempting logins. You should use generic messages like “Incorrect username or password” as not to specify when a user got half of the query right. If an attacker tries a brute force attack to get a username and password and the error message gives away when one of the fields are correct then the attacker knows he has one of the fields and can concentrate on the other field.
05. Server side validation/form validation
Validation should always be done both on the browser and server side. The browser can catch simple failures like mandatory fields that are empty and when you enter text into a numbers only field. These can however be bypassed, and you should make sure you check for these validation and deeper validation server side as failing to do so could lead to malicious code or scripting code being inserted into the database or could cause undesirable results in your website.