Error-Based SQL Injection: Detection, Exploitation & Protection

What is Error-Based SQL Injection?

Error-Based SQL Injection is a technique where attackers exploit database errors to extract information about the database structure. When an application does not handle SQL errors properly, the database may return detailed error messages that reveal critical insights, making it easier for attackers to craft further SQL injection attacks.

How Does Error-Based SQL Injection Work?

Attackers deliberately manipulate SQL queries to generate database errors, which can expose valuable information. By injecting malicious input, they force the database to return error messages containing details about the database structure, table names, or stored data.

Steps of an Error-Based SQL Injection Attack:

1. Finding a Vulnerable Input Field – Attackers identify an application input field where SQL queries are executed improperly, such as login forms, search bars, or URL parameters.
2. Injecting Malicious SQL Code – The attacker crafts an SQL payload that deliberately triggers an error message from the database.
3. Extracting Information from Error Messages – The attacker analyzes the returned error message to gather information about the database schema and refine further attacks.
4. Exploiting the Retrieved Information – Using the extracted details, attackers can construct precise queries to extract sensitive data.

Common Techniques Used in Error-Based SQL Injection

Using Syntax Errors

Attackers inject incorrect SQL syntax, such as an unclosed quote or an invalid keyword, to force the database to return an error message, revealing details about the database structure.

Example: Payload: ‘ (a single quote)

Possible Error Message:

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version 8.0.23 for the right syntax to use near ‘…’ at line 1

This reveals that MySQL is in use and even the specific version, aiding attackers in crafting targeted exploits.

Leveraging UNION Statements

Attackers deliberately mismatch the expected column count or data types in a UNION SELECT statement to trigger an error message. These errors help them understand the database structure.

Example: Payload: ” UNION SELECT 1,2 —

Possible Error Message:
The used SELECT statements have a different number of columns This indicates the number of expected columns, allowing attackers to adjust their query accordingly.

Using Database-Specific Functions

Attackers exploit built-in functions of different database systems to trigger errors that reveal details about the database environment.

Example: Payload: ‘ AND EXTRACTVALUE (1, CONCAT (0x7e, VERSION ())) –

Possible Error Message: XPATH syntax error: ‘~8.0.32’

This reveals that the database is MySQL 8.0.32.

Enumerating Columns with ORDER BY

By incrementally increasing the ORDER BY value in queries, attackers determine the number of columns in a table.

Example: Payload: ORDER BY 100—

Possible Error Message: Unknown column ‘100’ in ‘order clause

This indicates that the database has fewer than 100 columns, helping attackers refine their queries.

How to Prevent Error-Based SQL Injection

• Use Prepared Statements and Parameterized Queries: Prepared statements prevent SQL injection attack by ensuring user input is always treated as data, not SQL code.

Example:
cursor.execute(“SELECT * FROM users WHERE username = %s AND password = %s”, (username, password))

• Disable Detailed Error Messages: SQL errors can reveal database structure and table names. Log errors internally and display only generic messages like:
  “An error occurred. Please try again later.”
• Implement Web Application Firewalls (WAF): A Web Application Firewall (WAF) prevents error-based SQL injection attacks by filtering malicious SQL queries before they reach the database. It identifies known SQL injection patterns (e.g., OR 1=1 –, UNION SELECT) and blocks suspicious requests.

Additionally, WAFs analyze both request behavior and server responses to detect anomalies, suppressing detailed database error messages to prevent attackers from gaining insights into the database structure.

• Limit Database Privileges: The application’s database user should only have the minimum necessary privileges, restricting actions like DROP, ALTER, or INSERT to prevent severe damage even if an attack occurs.
• Regular Security Testing: Automated vulnerability scanners detect SQL injection risks, while penetration testing simulates real-world attacks to uncover blind spots. Regular testing helps identify and fix security gaps before attackers exploit them.

How AppTrana WAAP Prevents Error-Based SQLi

AppTrana WAAP provides robust protection against SQL injection—including error-based SQL injection—by analyzing both incoming requests and server responses to detect and block malicious activity. Unlike traditional WAFs that focus solely on filtering requests, AppTrana’s response inspection feature ensures that database error messages containing sensitive information—such as table names, column structures, and software versions—are masked, preventing attackers from gathering intelligence about the system. By implementing advanced response filtering and data masking, it ensures that even if a SQL query triggers an error, no exploitable details are exposed.

Additionally, AppTrana’s managed security team fine-tunes protection by creating custom security rules tailored to specific business needs, enforcing strict data handling policies, and updating defenses against evolving threats. Beyond attack prevention, AppTrana’s built-in DAST scanner actively scans web applications for SQL injection vulnerabilities, enabling businesses to identify and remediate security gaps before they can be exploited.