Understanding SQL Injection in Oracle SQL

Introduction

SQL injection is a type of web application security vulnerability where an attacker injects malicious SQL code into a web application’s database query. This can lead to unauthorized access, data tampering, or even complete control over the database.

In this article, we’ll explore how to avoid SQL injection in Oracle SQL by using parameterized queries and bind variables.

Understanding the Problem

The question at hand is: what characters need to be escaped in Oracle SQL to avoid SQL injection? The answer might seem straightforward at first glance, but it’s actually more complex than that.

The linked page we’ll be referencing for our explanation is SS64’s Syntax Escape. While this article provides a good starting point for understanding character escape in Oracle SQL literals, there are some important nuances to consider when dealing with dynamic SQL and user interfaces.

Character Escape

In Oracle SQL, character escape is used to prevent special characters from being interpreted as SQL keywords or syntax elements. For example, the single quote (’) is used to enclose string literals:

SELECT 'The woman''s hat blew off in the wind.' FROM DUAL;

To use a single quote within a string literal, you need to escape it with another single quote:

SELECT 'The woman''s hat blew off in the wind.' FROM DUAL;

Similarly, the ampersand (&) has special meaning in Oracle SQL and needs to be escaped when used as part of a substitution variable:

SELECT 'A&B' FROM DUAL;

In contrast, the at (@) symbol does not need escaping in SQL.

User Interface-specific Characters

Different user interfaces may have different escape characters or syntax rules for special characters. For example, in SQL*Plus, you can set an escape character using the SET ESCAPE command:

SET ESCAPE '\';

This allows you to use special characters without escaping them:

SELECT * FROM dual WHERE column LIKE '%\%%';

However, this is only valid in SQL*Plus and not in other user interfaces.

Conclusion

In conclusion, while it’s tempting to try to escape all characters to prevent SQL injection, that approach is actually counterproductive. Instead, use parameterized queries and bind variables to pass values into your queries.

Here are some best practices for avoiding SQL injection:

• Do not build queries by concatenating strings.
• Use parameterized queries with bind variables.
• If you need to dynamically provide a schema/table/column name, use DBMS_ASSERT to validate those object identifiers.
• Always follow the specific syntax and escape rules of your user interface.

By following these guidelines, you can write secure and reliable Oracle SQL code that avoids SQL injection vulnerabilities.

Additional Considerations

Dynamic SQL

When working with dynamic SQL, it’s essential to use parameterized queries and bind variables to prevent SQL injection. This involves passing values into the query as parameters rather than concatenating them into the query string.

Here’s an example of how to write a secure dynamic SQL query in Oracle:

DECLARE
  v_name  VARCHAR2(20);
  v_id    NUMBER;
BEGIN
  v_name := 'John Doe';
  v_id := 123;

  -- Parameterized query with bind variables
  FOR cur_rec IN (SELECT * FROM users WHERE name = v_name AND id = v_id) LOOP
    DBMS_OUTPUT.PUT_LINE(cur_rec.name);
  END LOOP;
END;

Substitution Variables

Substitution variables are a feature of Oracle SQL that allows you to define values that can be used within a query. However, substitution variables can also introduce security vulnerabilities if not used properly.

Here’s an example of how to use substitution variables securely:

DECLARE
  v_name  VARCHAR2(20);
BEGIN
  -- Define a substitution variable
  DBMS_ASSERT(v_name IS NOT NULL);

  -- Use the substitution variable in a query
  FOR cur_rec IN (SELECT * FROM users WHERE name = v_name) LOOP
    DBMS_OUTPUT.PUT_LINE(cur_rec.name);
  END LOOP;
END;

By following these best practices and guidelines, you can write secure and reliable Oracle SQL code that avoids SQL injection vulnerabilities.

Last modified on 2023-05-19