While it is difficult to completely prevent SQL injection attacks, the following measures can significantly reduce the risk to your applications.
Prepared statements are a method of protecting against SQL injection attacks. They allow the programmer to define a parameterized query in advance, and then supply the data to be used in the query at runtime. The database then separates the data from the query, which helps prevent any malicious input from being interpreted as part of the SQL command.
This is a more secure way of executing dynamic SQL queries compared to concatenating the query string and input data, which is vulnerable to SQL injection. By using prepared statements, the risk of SQL injection can be reduced, as the input data is treated as separate from the SQL query, and any special characters or escape sequences are handled correctly by the database.
Stored procedures are pre-compiled sets of SQL statements that are stored in the database and can be called as a single executable unit. When a stored procedure is executed, the database first compiles the procedure and then executes the compiled code. This means that any dynamic SQL statements within the stored procedure are parsed and optimized only once, when the stored procedure is first created, rather than each time the procedure is executed.
Stored procedures provide an additional layer of security against SQL injection, as the SQL statements within the stored procedure are protected from tampering by end-users. Additionally, stored procedures can enforce a specific set of business rules, reducing the risk of rogue SQL statements being executed.
Principle of Least Privilege
The principle of least privilege is a security concept that states that an application should only have the minimum necessary permissions to carry out its intended functions. In the context of SQL injection attacks, this means limiting the permissions of the application when interacting with the database to reduce the risk of an attacker using SQL injection to execute malicious actions.
Applications should be designed to only have access to the resources they need. For example, applications can be configured to execute DML statements but not DDL statements, or to execute with read-only permissions. This restricted privilege can help prevent an attacker from modifying the database structure or executing rogue SQL statements.
Allowlist Input Validation
Allowlist input validation is a method of protecting against SQL injection attacks by checking the input data to ensure it is valid and allowed. This approach involves defining a set of acceptable inputs, also known as an "allowlist," and only accepting data that meets the criteria in the allowlist. Any input that does not match the allowlist is rejected.
For example, if a search field only allows alphanumeric characters and spaces, any input that contains special characters or escapes sequences would be rejected. This helps prevent malicious code from being interpreted as part of an SQL statement, and therefore reduces the risk of SQL injection.
Allowlist vs. denylist
Allowlist input validation provides a more secure method of input validation compared to denylist input validation, where a list of unacceptable inputs is defined and all other inputs are accepted. The problem with denylist validation is that attackers can easily bypass the validation by using inputs that are not on the denylist.
By using allowlist input validation, the risk of SQL injection can be reduced, as malicious input that does not match an acceptable value will not be processed by the application. This helps to prevent attackers from inserting malicious code into an SQL statement and executing unauthorized actions.
However, it's important to keep the allowlist up-to-date and comprehensive to ensure that it covers all possible legitimate input values, otherwise it may cause false positive results or prevent legitimate input from being processed.