Sunday, February 5, 2017

Beginning Web Application Testing: Detecting OS Command Injection - DVWA

As stated in the previous post, in order to be able to log web traffic via “POST” method and at least from Apache perspective, we needed to enable “mod_dumpio”. Take a look at the previous post for guidance on how to perform that configuration.

Let’s get into the meat of things right away.

First it is important to note that this logging is being done in “debug” mode. As a result there is a large volume of data in these logs for the investigation we need to do. So let’s focus on what is important or to look at it another way, let’s focus on our indicator here which is IP address “”.

Using “cat CommandInjection.logs | grep "mod_dumpio" | grep --perl-regexp "" --colour=always | more” we see the first snapshot of our input which was “-n+1+-l+4000+” when encoded. The image below show both the input and output for this first activity.

While going through the log this way may prove helpful, for demonstration purposes and in the interest of time, let’s look at it from a different perspective.

Let first look at all the input which came in and we can do this via this one-liner “cat --number CommandInjection.logs | grep --perl-regexp "dumpio_in" | grep --perl-regexp ":\s+ip=.*?\&" --only-matching | sort | uniq --count | sort --numeric --reverse”.

From above we see there were a total of 16 requests which came in. One of them occurring 4 times, another 2 times and the rest 1 time.

The same method which was used to decode the logs in the blog entry on detecting Cross Site Scripting (XSS) can be used to decode these logs. Alternatively, we could simply copy this text, paste it into something like “Notepad++” or another decoder tool of your choice.

The image below shows “Notepad++” URL decoding of the input.
URL Decode - Command Injection

Now that we have the input, let’s see if and or what our server returned.

Starting off with the attempt to kill the “VBoxService.exe”, let’s use “grep” to make this easier for us to understand if our server returned anything. Using “
cat --number CommandInjection.logs | grep --perl-regexp "\s+The\sprocess.*?\<|taskkill.*?\&" --colour=always” we get a clear view that the command was executed successfully as shown below. Thus the process was terminated.

Let’s now take a look at the attempt to add the “webHack” user to the “Administrators” group. Once again, let’s use “grep” to make this easier via the following “cat --number CommandInjection.logs | grep --perl-regexp "net+.*?\&|The\s+command.*?\." --colour=always | more”.

Above we see the user “webHack” is successfully added to the system. Next step is to validate whether or not the user actually got created. The image below shows it was successfully created and this was confirmed via “cat --number CommandInjection.logs | grep --perl-regexp "net\+.*?\&|The\s+command.*?\.|webHack" --colour=always | more”.

Next we see the user being successfully added to the “Administrators” group.

Finally we see the validation that the user was successfully added. This can be seen via “
cat --number CommandInjection.logs | grep --perl-regexp "net\+.*?\&|The\s+command.*?\.|webHack" --colour=always | more

command injection - validate user is an administrator

Ok then! That’s it for detecting command injection. On to the next post SQL Injection.

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