Securing your MS SQL Server: Defending against SQL Injection Attacks

Securing your MS SQL Server against injection attacks requires you to take various measures. These include enforcing least-privilege access, using parameterized queries, applying regular windows and server patches, sanitizing user inputs, and restricting database procedures. In this article, we will explain these security measures and techniques in detail. We will also mention a reliable SQL recovery tool that can assist you in recovering data, if your database is compromised.

What are SQL Injection Attacks?

SQL injection attacks are one of the most common types of attacks used by hackers to exploit the SQL servers to extract sensitive information. They use SQL queries with user input to exploit web applications or databases. SQL injection (SQLi) is a technique for code injection used by attackers to inject malicious code into the application, allowing them to view the sensitive data or modify the data in database. In SQL injection attacks, SQL commands are inserted into the input so as to affect the execution of normal commands to get the sensitive data that the application should not have returned.

In SQL injection attack, the attacker cannot access the complete data from the database but they can add various commands, such as Insert, Modify, and Delete to change the data. Such attacks could also lead to the execution of administrative operations, access to the file system, and to install and execute malware.

The following vulnerabilities can lead to SQL injection attacks:

• Lack of input validation
• Inadequate escaping of user input
• Unpatched software

Attackers often target specific parts of SQL statements through points like:

• Use WHERE clauses in SELECT queries to manipulate conditions to retrieve unauthorized data.
• Use UPDATE statements to alter or delete records.
• Table or column names in queries to Inject code in them to change the structure or target of queries.

Without any input validation, the attacker can send SQL code to change the logic of SQL queries.

How SQL Injection Attacks Work in MS SQL Server?

Microsoft SQL Server runs all the queries whose syntax is correct. It can even execute dynamically constructed SQL statements by attackers, if they are not secured. Here, SQL injection can be done by passing the parameters to a query, instead of values. For example, the OR operator or the UNION operator.

Here are some examples of injection techniques that can help you understand how SQL injection attack works.

1. Always True Technique

It is one of the popular SQL injection techniques used by attackers against SQL Server. In this technique, they change a condition in the query so it always return value without validation.

Let’s take an example. Suppose, a web application uses the following SQL statement to retrieve customers’ data from the database:

The character “?” represents your customer code used to access the data. Without any protection, anyone can write in the parameter “?” a code plus the string "OR ""=", passing an always-true logical condition in the statement (see the below example).

The above command will return the data about all the customers. This technique is called Always True Technique.

2. Batched SQL Injection

Another way to execute SQL injection is to take advantage of the fact that SQL can execute multiple statements at a time through a batch. A batched SQL injection adds another statement to the original statements. For example, in the previous statement, the following statement is added:

The complete statement will be:

This command will drop the customers table.

What are the Different Types of SQL Injections?

There are various types of SQL injections, based on the methods used to access the data and their impact. Let’s discuss some common ones.

1. In-band SQL Injection

In In-band Injection, attacker uses the same communication channel to launch the attack and collect the results. There are two types of In-band Injections in SQL. These are:

• Error-based Injection: It relies on the error messages, which are thrown by server to determine information about the objects of the database.

• Union-based Injection: It works on the UNION operator to collect all the information about different statements.

2. Inferential SQL Injection

In this type of SQL injection, a data payload is sent to the server to observe behavior and response to retrieve the structure of the MS SQL database. Inferential injection is classified into Boolean-based and Time-based. In Boolean-based inferential injection, the attacker sends SQL queries to force the application to return a Boolean result to blindly determine the presence of vulnerabilities in the MS SQL Server engine.

In the Time-based inferential injection, the attacker forces the application to return generic errors. This led the database to pause for a specific time. The response time helps the attacker to identify the query returns.

3. Out-of-Band SQL Injection

In this type of attack, the attacker is not able to use the same channel to launch the attack and sum up the results. The attacker uses MS SQL functions, like xp_dirtree, to force the application to transmit data through a protocol network and read information.

How to Secure MS SQL Server against SQL Injection Attacks?

Securing your MS SQL Server against SQL injection attack is crucial to safeguard data, comply with regulations, maintain business continuity, protect your organization's reputation, and mitigate the financial and legal risks associated with security breaches. To secure and protect your SQL Server against SQL injection attacks, you can take the following steps:

1. Use Parameterized Queries

A query is called parameterized if one or more parameters are defined and used as placeholder and provided at the time of execution.

2- Use Prepared Statements

You can use a prepared statement with a parameterized query to mitigate the chances of SQL injection attack. Parameters should have predefined name and the type of data. For example, if you define a parameter as an integer type, you will not be able to add OR or UNION operators.

3. Use Input Validation

Input validation refers to the process of inspecting and validating data provided by external sources to ensure it is according to the expected formats, data types, and various constraints, before using in the system.

4. Use Sanitization

Sanitization is an ensemble of methods used to prevent SQL injection attack. Sanitization of the input values means removing or escaping any characters that could be interpreted as SQL commands or keywords. It is in fact necessary to pay attention to the special characters, such as quotes, semicolons, dashes, and comments.

5. Follow Principle of Least Privilege

The principle of least privilege (PoLP) is a well-known concept of information security. This concept states that “a user must be given minimum level of access (or permissions) needed to perform the job.” Limiting permissions during the interaction with the database reduces the risk of SQL injection. Administrative privileges must be avoided first and the database users and systems must be grouped based on their roles.

You can have these groups:

• Users who require access just to read and export data from the database.
• Users who can read and write to specific schema (edit access).
• Privileged users who can add and delete the schema (data definition language).
• Privileged and administrative users who can add and grant access rights to various users.

Here, the users under particular groups are granted privileges necessary to perform their duties. Privileged users are also split into two groups because the users who can modify schema do not always require privileges to grant access rights. Similarly, they cannot be grouped under the users who can just read and write.

Privileged users with administrative access should have two accounts: A user account for normal database access and an admin account for adding users or assigning duties.

6. Use Web Application Firewall (WAF)

Web Application Firewall or WAF is an application designed to protect against SQL injection attacks. WAF monitors and filters the network traffic against attacks in the application code and server structure. WAF is a component of fundamental importance and can prevent assaults on web application vulnerabilities, help prevent data theft, service interruption, and reputational harm.

Some popular WAF solutions in the market are:

• Cloudflare: Cloud-based WAF with CDN integration
• Fortinet FortiWeb: Best all-around threat protection
• Microsoft Azure Application Gateway: Best for Azure

MS SQL Server Security Best Practices for Preventing SQL Injection

After following all the measures and steps mentioned above, you should also follow the below practices.

Regular Testing and Auditing

You must do regular security testing and auditing of your MS SQL Server.

Identify and Address Potential SQL Injection

You can do vulnerability assessment using various software. You can use the vulnerability assessment function available in the SQL Server Management Studio (SSMS). Some other free software for this purpose are jSQL Injection and SQL Map.

Encrypt the Data

Encryption can protect against SQL injection in an indirect way. Encrypting the database does not block SQL injection attacks but it will reduce the damage by limiting the value of the extracted data.

Follow Secure Coding Practice

Secure coding practices must be applied by default even if you have a WAF. As mentioned above, you must apply Input validation to ensure that only properly formed data is entered by users. In addition, proper error handling is of fundamental importance. If errors are not managed correctly, security problems can arise.

Use Secure Libraries

It is also suggested to use secure libraries and frameworks. These coding libraries and software frameworks are pre-built, tested, and secure. These can help avoid attackers taking advantage of even the tiniest of issues in code made from scratch. A famous library is OWASP’s Proactive Control C2.

What If SQL Injection Attack cause Database Damage or Corruption?

The infected code by SQL injection can delete, alter, or drop tables in database, or execute bulk complex commands. This can also lead to corruption in SQL Server database. If the database gets corrupted, you can restore the backup. If the backup is corrupted or its not available then you can use Stellar Repair for MS SQL - a specialized SQL repair software designed for handling SQL database corruption. This powerful and easy-to-use software employs intelligent algorithms that are able to detect and resolve corruption issues. It is able to recover all the MS SQL database objects, such as procedures, triggers, views, etc. with complete integrity. It supports all the SQL Server versions, including the latest SQL 2022 version.

Conclusion

Above, we have explained SQL injection in detail and how to secure your SQL Server and database from SQL injection attacks. You can implement the discussed best practices and continuously monitor the security of the server to prevent it against SQL injection attacks. In case the database gets corrupted, you can use Stellar Repair for MS SQL – one of the best software to repair corrupt SQL database and recover all the data.