- SQL injection, also known as SQLI, is a common attack vector that uses malicious SQL code for backend database manipulation to access information that was not intended to be displayed.
- It generally allows an attacker to view data that they are not normally able to retrieve. This might include data belonging to other users, or any other data that the application itself can access.
- In many cases, an attacker can modify or delete this data, causing persistent changes to the application's content or behaviour.
Impact of a successful SQL injection attack
A successful SQL injection attack can result in unauthorized access to sensitive data, such as passwords, credit card details, or personal user information. Many high-profile data breaches in recent years have been the result of SQL injection attacks, leading to reputational damage and regulatory fines. In some cases, an attacker can obtain a persistent backdoor into an organization's systems, leading to a long-term compromise that can go unnoticed for an extended period.
SQL injection examples
There are a wide variety of SQL injection vulnerabilities, attacks, and techniques, which arise in different situations. Some common SQL injection examples include:
Retrieving hidden data, where you can modify an SQL query to return additional results.
Subverting application logic, where you can change a query to interfere with the application's logic.
UNION attacks, where you can retrieve data from different database tables.
Examining the database, where you can extract information about the version and structure of the database.
Blind SQL injection, where the results of a query you control are not returned in the application's responses.
Detection of SQL injection vulnerabilities
The majority of SQL injection vulnerabilities can be found quickly and reliably using Burp Suite's web vulnerability scanner.
SQL injection can be detected manually by using a systematic set of tests against every entry point in the application. This typically involves:
Submitting the single quote character ' and looking for errors or other anomalies.
Submitting some SQL-specific syntax that evaluates to the base (original) value of the entry point, and to a different value, and looking for systematic differences in the resulting application responses.
Submitting Boolean conditions such as OR 1=1 and OR 1=2, and looking for differences in the application's responses.
Submitting payloads designed to trigger time delays when executed within an SQL query, and looking for differences in the time taken to respond.
Submitting OAST payloads designed to trigger an out-of-band network interaction when executed within an SQL query, and monitoring for any resulting interactions.
SQLI prevention and mitigation
There are several effective ways to prevent SQLI attacks from taking place, as well as protecting against them, should they occur.
- The first step is input validation (a.k.a. sanitization), which is the practice of writing code that can identify illegitimate user inputs.
- Most instances of SQL injection can be prevented by using parameterized queries (also known as prepared statements) instead of string concatenation within the query.
