SQL Injection Testing

SQL injection testing requires understanding an application’s interaction with a database server to access data. Applications often communicate with a database to authenticate web forms (checking credentials against the database) and perform searches (user-submitted input can extract data from the database via SQL queries). Testers must list the input fields with values that could end up in an SQL query. 

Usually, the first test involves adding a quotation mark or semicolon to a parameter or field. If the application doesn’t filter the input, the value in quotation marks could produce a flawed query, while the semicolon could produce an error. 

Additionally, testers can try altering a query using SQL keywords (such AND and OR) and comment delimiters like — and /* */. To produce an error, they can substitute a string for a number. The testers should keep track of each response from the web server and look at the source code. Without informing the user, the responses can be flawed. Testers can successfully reproduce an injection attack with the help of proper error messages, which contain invaluable information.

Unfortunately, applications do not always provide the full details of an error, issuing simple 500 errors. In these cases, testers must use blind SQL injection methods. Testers should check every field individually to identify the vulnerable parameters.

Here are some of the testing methods to help identify SQL vulnerabilities: 

1. Stacked Query Testing

In the stacked query method, testers complete an SQL statement and write a new one. Testers and developers should ensure that their applications do not support stacked queries (where possible). For example, developers should avoid using a multi-query statement that enables stacked queries.

2. Error-Based Injection Testing

Error-based injection takes advantage of the user-visible SQL error messages. Users make an effort that almost certainly results in an error and then extract information from the generated error message. Users who have access to details like table names can corrupt the underlying database more easily.

To prevent error-based injection attacks, teams must ensure the application never displays internal SQL errors to the user. The application should handle errors internally. 

3. Boolean-Based Injection Testing

The boolean method involves appending conditions to conditional statements (true in some cases, false in others). Attackers can perform several conditional queries to learn about the database. Testers can use this attack method to identify boolean-based injection vulnerabilities.

To prevent boolean-based injection attacks, teams must ensure the application never runs user input as SQL code. One way to achieve this is with prepared statements that ensure SQL does not interpret user input as code. 

4. Out-of-Band (Blind) Exploit Testing

Out-of-band exploit tests are useful for assessing blind SQL injection vulnerabilities, where the attacker doesn’t know anything about the operation’s outcome. This method uses Database Management System (DBMS) functions to perform out-of-band connections and deliver query results to the attacker’s server. 

5. Time Delay Exploit Testing

Time delay exploits are useful for blind SQL injection situations. This method involves sending injected queries and monitoring the server’s response time (if the conditional is true). A delayed response indicates that the conditional query’s result is true.

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