SQL injection (SQLi) is one of modern web applications’ most serious security threats. It enables malicious users to inject malicious code into a database to gain access to confidential information, modify or delete data, or even take control of the entire system. Therefore, knowledge and awareness of how SQLi attacks work and how they can be prevented are essential for securing any modern web application.
What Is an SQL Injection Attack?
An SQL injection attack is a malicious code injection that exploits application vulnerabilities. When successful, this attack can allow cybercriminals to:
- Access sensitive data
- Perform admin tasks on the database
- Alter database information
- Recover files from the system
In some cases, attackers may even be able to issue commands to the underlying database operating system. Database administrators must be aware of these threats and take proactive steps to secure their applications from such attacks.
How does an SQLi attack work?
SQLi attacks work by injecting malicious code into an application’s Structured Query Language (SQL) queries. Such attacks are made possible when a website or web application does not correctly validate user input before the server processes it. By exploiting specific vulnerabilities in the application, attackers can gain access to secure parts of the database or modify existing data.
The impact of an SQLi attack
Successful SQLi attacks can have severe impacts on organizations of all sizes. Attackers may be able to steal credentials and access databases containing sensitive customer information such as credit card numbers, Social Security numbers, or other personal data. They may also be able to alter or delete existing data to disrupt service or manipulate records for financial gain. Additionally, attackers can use these attacks as part of a more extensive campaign for lateral movement within a network.
6 Expert Tips For SQLi Mitigation
The Open Web Application Security Project (OWASP) has the best tips for SQLi in its SQL Injection Prevention Cheat Sheet. The primary and secondary defenses they identify—including use of prepared statements and stored procedures, and conducting allowlist input validation—are summarized below.
Primary defense 1: Use of prepared statements (with parameterized queries)
The use of prepared statements with variable binding (also known as parameterized queries) should be the first line of defense for mitigating SQL injections. Such a coding style lets developers define all of the SQL code initially and then pass each parameter to the query later, thus allowing the database to differentiate between code and data, no matter what user input is used.
The benefit of prepared statements is that they prevent attackers from altering a query’s intent even if they insert malicious SQL commands. In addition, the easier writing structure of these queries makes them simpler for developers than dynamic queries.
Primary defense 2: Use of properly constructed stored procedures
Stored procedures are snippets of SQL code stored and run in the database, which reduces the need to embed SQL code in the application layer. Stored procedures can also be set up to accept user input, reducing the burden of validating user input within the application.
Using properly constructed stored procedures is important to keep in mind when mitigating SQLi risks. While it is true that not all stored procedures are immune to exploitation, utilizing standard stored procedure programming, constructs that automatically parameterize any SQL statement, can be highly effective in protecting against potential attacks.
Using prepared statements and stored procedures ultimately leads to the same outcome—successful protection from exploitative SQLi attempts—as long as the developer takes measures to ensure sound construction and execution.
Primary defense 3: Allowlist input validation
Many parts of SQL queries are not intended to use bind variables, such as table or column names, and sort order indicators, like ascending order (ASC) or descending order (DESC). In these cases, the best approach is validating inputs against the allowlist.
If user parameter values are used to determine table names and column names, then these parameters should be cross-referenced with the expected or legal values to ensure there are no unvalidated user inputs in the query.
Allowlist input validation can go a long way in preventing security breaches due to malicious inputs; however, if possible, it’s recommended to consider rewriting the code altogether, as this could be a symptom of bad coding design.
Primary defense 4: Escaping all user-supplied input
Escaping all user-supplied input is a technique that should be used as a last resort when the first three defenses above are not feasible. Escaping user input before putting it into a query, while effective, is often database-specific in its implementation and should be applied with caution since it cannot be guaranteed that it will protect from all types of SQL injection in all situations. Escaping user input is typically recommended for legacy code when implementing input validation isn’t cost-efficient.
Additional defense 5: Enforcing least privilege
To ensure the security of data environments, administrators must minimize the privileges assigned to each database account. It may be convenient to give an application user database administrator (DBA) access or admin-type rights, but this practice will likely create weak points in the network.
To ensure all access rights are suitable and secure, it’s suggested that administrators start from the basics and figure out what access is required rather than trying to limit existing privileges. Each account should only have read access for specific tables, if necessary. This helps prevent unnecessary exposure of data in case of attack attempts.
Instead of providing access to the entire table, if an account only needs a specific portion, it’s better to create a view that limits their access and assigns them privileges for this particular view. To ensure data security, it’s recommended not to grant access to any accounts with “create” or “delete” capabilities whenever possible.
To ensure a secure database, the IT department should develop a policy that requires storing procedures while limiting application accounts from executing queries directly. Furthermore, these restricted accounts should only be able to execute necessary stored procedures and should not be granted access to any tables in the database.
With SQLi, attackers can manipulate authorized parameter values and gain entry into information they otherwise wouldn’t be able to, but that the application itself might be allowed access to. Therefore, reducing the privileges given to your applications can significantly reduce the risks of unapproved access attempts.
Additional defense 6: Performing allowlist input validation as a secondary defense
Performing allowlist input validation prevents the spread of attacks and serves as an additional layer of security for those who use SQL databases regularly. When implemented as a secondary defense, it should be able to detect and prevent the injection of unauthorized input before it is passed to the SQL query.
Input validation is vital in ensuring that only valid data enters the workflow and that there are minimal chances of malfunctions due to malformed data persisting in the database. This type of defense should preferably be carried out as soon as possible when data is received from any external source. Both syntax and semantic levels should be assessed for further accuracy.
SQL Injection Example
To understand how an SQLi attack can occur, it may help to review an example. Consider this scenario.
An attacker is trying to gain unauthorized access to the database used by an online store. They craft a malicious input that gets injected into an unprotected SQL query, allowing the attacker to extract confidential information stored in the database and modify it as they please.
For example, let’s say the SQL query looks like this:
SELECT * FROM users WHERE username = ‘$username’ AND password = ‘$password.’
The attacker would craft a malicious input like this:
Username: 1′ or ‘1’ = ‘1
Password: 1′ or ‘1’ = ‘1
This modified SQL query would now look like this:
SELECT * FROM Users WHERE Username=’1′ OR ‘1’ = ‘1’ AND Password=’1′ OR ‘1’ = ‘1’
The hacker has effectively injected an OR condition into the authentication process. Worse, the condition ‘1’ = ‘1’ is always true, so this SQL query will always result in the authentication process being bypassed.
This modified SQL query would return all of the records from the ‘Users’ table, regardless of whether a valid username and password had been provided. This is one of the most common methods attackers can use to gain unauthorized access to sensitive information.
Using characters like “;” to append another query onto the end of an existing one and “–” to comment out and therefore cut off a part of an existing query, a hacker could potentially delete entire tables or change the data they contain. They could even issue commands to the underlying operating system, thereby taking over the machine and using it as a staging post to attack the rest of the network.
What Is the Goal of an SQL Injection Attack?
There are four main goals of an SQLi attack: compromising data confidentiality as well as data integrity, stealing data, and ultimately compromising the entire network.
- Compromise data confidentiality: An attacker can use an SQLi attack to access confidential data stored in a database, such as credit card information and passwords.
- Compromise data integrity: A hacker can manipulate or delete data stored in a database without authorization. This could lead to the theft of sensitive information or even distributed denial-of-service (DDos) attacks on systems that rely on the data integrity of the database.
- Steal data: Data theft is one of the most common goals of an SQLi attack. Attackers can use this type of attack to steal login credentials and other sensitive information from databases.
- Compromise the entire network: An SQLi attack can grant hackers access to other parts of a network by using the hijacked database as a staging post. The attacker could then launch further attacks on other systems or networks connected to the network.
Bottom Line: Protecting Networks From SQL Injection Attacks
SQL injection is one of the most common web application security threats and can have severe consequences if not addressed. To protect against these attacks, organizations should implement input validation and parameterized queries as part of their overall security strategy.
Additionally, it is crucial to ensure all databases are properly configured and regularly updated with the latest patches. By implementing effective SQLi mitigation strategies, organizations can significantly reduce the risk of being compromised by an attack.