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Common Error Based Payload Attacks on SQL Servers

SQLi, short for SQL injection is a critical web security vulnerability that enables attackers to interfere with the database queries executed by an application.

This manipulation allows attackers to access restricted data, such as information belonging to other users or sensitive application data, potentially altering or deleting it.

Error-based SQL injection is a specific in-band technique within SQLi that exploits error messages provided by the database server, allowing attackers to gather insights into the database structure, tables, and even data without requiring direct access to query results.

Today we are going to take a closer look at Error-Based SQL Injections and how they can affect SQL servers.

An Overview:

• What is Error-Based SQL Injection?
• How Error-Based SQL Injection Attacks Work
• 1. Intentionally Triggering SQL Errors
• 2. Leveraging SQL Server Error Functions
• 3. Using Invalid Column or Function Names
• 4. Hexadecimal and Character Conversion Attacks
• Example of Error-Based Payloads
• Common SQL Server Functions Used in Error-Based SQL Injections
• Mitigating Error-Based SQL Injection Attacks
• Identifying Vulnerable SQL Server Applications

What is Error-Based SQL Injection?

Error-based SQL injection takes advantage of database error messages to extract valuable information. When crafted correctly, SQL statements can trigger specific database errors that reveal details about the structure and contents of the database.

For instance, error messages may expose table names, column names, and data types, enabling attackers to develop more sophisticated queries for further exploitation.

This method is effective because it doesn’t require direct access to data. Instead, attackers analyze the error messages generated by forced syntax errors or invalid operations, such as division by zero, which prompt the database to reveal otherwise hidden details.

How Error-Based SQL Injection Attacks Work

In an error-based SQL injection attack, the attacker intentionally triggers errors in the database to extract information. These errors are usually crafted through specific SQL payloads designed to provoke detailed responses. Here’s a breakdown of common techniques and their functions.

1. Intentionally Triggering SQL Errors

Attackers create SQL statements with syntactical or logical errors, such as division by zero (`1/0`), to induce an error response from the SQL Server.

Then, the server returns an error message that may reveal sensitive database details, such as query structure or table names.

2. Leveraging SQL Server Error Functions

SQL Server includes built-in functions that generate specific error responses when misused. Attackers exploit these functions to obtain information about the database structure or server configuration.

Functions like `@@version` reveal the SQL Server version, which can offer insights into potential vulnerabilities.

3. Using Invalid Column or Function Names

By referencing non-existent columns or functions in SQL queries, attackers force the server to produce an error message. This message may contain valuable hints about the database schema, which attackers can use to form more accurate queries.

4. Hexadecimal and Character Conversion Attacks

Attackers can encode their payloads or convert data into hexadecimal or ASCII character formats to bypass filters or manipulate error-based injections for further exploitation.

Example of Error-Based Payloads

An error-based SQL injection payload may look like this:

(select 1 and row(1,1)>(select count(*), concat(@@version,0x3a,floor(rand()*2))x from (select 1 union select 2)a group by x limit 1))


This query introduces forced errors to retrieve data about the SQL Server version, allowing attackers to gather insights for future attacks.

Common SQL Server Functions Used in Error-Based SQL Injections

• @@version

  This reveals the SQL Server version and operating system details.

  SELECT @@version;
• DB_NAME()

  It returns the name of the current database, helping attackers understand the database structure.

  SELECT DB_NAME();

• USER_NAME()

  It shows the current user’s name, which can expose privilege levels.

  SELECT USER_NAME();
• CHAR()

  It converts integers into ASCII characters. Often used to encode error messages or bypass input validation filters.

  SELECT CHAR(113) + CHAR(114) + CHAR(115); -- returns 'qrs'

Mitigating Error-Based SQL Injection Attacks

Error-based SQL injection can lead to significant data breaches if left unaddressed. To prevent such attacks:

• Use parameterized queries to ensure SQL statements are isolated from user input, which helps eliminate vulnerabilities.
• Apply strict input validation to avoid processing unexpected characters or values.
• Configure the database and application to show generic error messages, preventing attackers from viewing sensitive error details.
• Patching databases and application software ensures that you’re protected against known vulnerabilities.

Identifying Vulnerable SQL Server Applications

Without a doubt, testing for vulnerability to error-based SQL injection is a critical step in safeguarding SQL Server applications.

To check if an application is susceptible, start by examining input fields, such as search bars, login forms, and comment sections, where users can enter data that gets processed by the database.

Additionally, injecting special characters, such as single quotes (`’`) or double quotes (`”`), can help identify potential vulnerabilities; if a database error appears in response, it’s an indication the application may be processing input unsafely.

Also, visible error messages, like “SQL syntax error” or “Unclosed quotation mark after the character string,” are another sign of vulnerability. These messages often reveal details about the database’s structure, helping attackers craft more targeted injection attacks.

We can further test for error-based vulnerabilities by introducing statements like `1/0` or non-existent column names, which can force the SQL Server to produce detailed error messages. Error functions like `@@version` and `DB_NAME()` are commonly used in these tests to retrieve sensitive information through error messages.

Automated tools like SQLMap and Burp Suite are also highly effective in identifying SQL injection vulnerabilities. By automating payload injection and testing various SQL commands, these tools can quickly assess if an application’s SQL queries are prone to error-based SQL injection, ensuring any risks are detected early.

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Conclusion

By following the above security practices, we can protect our application from error-based SQL injection attacks and safeguard our users’ data from potential exploitation.

In brief, our Support Experts introduced us to error based Payload attacks on SQL Servers.