This type of blind SQL injection relies on the database pausing for a specified amount of time, then returning the results, indicating successful SQL query executing. Using this method, an attacker enumerates each letter of the desired piece of data using the following logic:
The query returns either true or false. If we obtain true, then we have completed the inference and, therefore, we know the value of the parameter. If we obtain false, this means that the null character is present in the value of the parameter, and we must continue to analyze the next parameter until we find another null value.The blind SQL injection attack needs a high volume of queries. The tester may need an automatic tool to exploit the vulnerability.
bsqlbf 1.1 – Blind SQL Injection Tool
Alternatively, one may play lucky. That is the attacker may assume that there is a blind or out-of-band SQL injection vulnerability in a the web application. He will then select an attack vector (e.g., a web entry), use fuzz vectors (1) against this channel and watch the response. For example, if the web application is looking for a book using a query
There is one more possibility for making a blind SQL injection attack when there is not visible feedback from the application: by measuring the time that the web application takes to answer a request. An attack of this sort is described by Anley in ([2]) from where we take the next examples. A typical approach uses the waitfor delay command: let's say that the attacker wants to check if the 'pubs' sample database exists, he will simply inject the following command:
However, it might happen that the command waitfor is not available (e.g., because it is filtered by an IPS/web application firewall). This doesn't mean that blind SQL injection attacks cannot be done, as the pen tester should only come up with any time consuming operation that is not filtered. For example
Blind SQL Injection vulnerabilities are by no means the most easily exploitable SQL injections while testing real-life applications. In case of recent versions of MS Access, it is also not feasible to execute shell commands or read/write arbitrary files.In case of blind SQL injections, the attacker can only infer the result of the query by evaluating time differences or application responses. It is supposed that the reader already knows the theory behind blind SQL injection attacks, as the remaining part of this section will focus on MS Access specific details.The following example is used:
Let's consider the myId parameter vulnerable to blind SQL injection. As an attacker, we want to extract the content of column 'username' in the table 'users', assuming that we have already disclosed the database schema.A typical query that can be used to infer the first character of the user-name of the 10th rows is: 2ff7e9595c
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