Parameters 4 and 5 may require some more explanation. If you want to skip the first 10 of these strings, and start fuzzing at string 11, you can set SKIPSTR to 10 again, counting starts from 0. To write a SPIKE script for our fuzzing exercise, we first need to know what some of the available commands are and what they do. If you want to hunt through the SPIKE distribution directory, the available primitives that we can use as commands in our script file can be discovered by examining some of the example.
The spike. Keep in mind that the SPIKE scripting capability will only support a subset of the primitives in spike. To save you the trouble of hunting through those files, I will list some of the more useful SPIKE primitives for scripting below. I have broken the commands below into a number of high level categories relating to strings, binary data, blocks and other useful functions. They support a wide variety of ways to specify the binary data. For the binary commands in SPIKE, various other methods for specifying the same data are also available.
Any added white space is also ignored. All of this combines to allows easy cutting and pasting from a variety of different applications that represent data in Hex format, such as packet capture tools, debuggers, etc.
Defining blocks Block defining commands allow you to specify the start and end points of a named block within a SPIKE script. Block sizes Block size commands allow you to insert the size of data inside a named block inside the SPIKES generated by your script, using a variety of different size formats.
There are other methods too, that can allow you to represent block size in a large variety of formats, and some that even allow you to add preset values to the block size before it is. To see some of the other options, simply perform a grep on the spike. One particularly useful function is printf , which can be used to output data to the terminal, which can give our scripts more informative console output.
This size field will be automatically updated as the fuzz string changes. Successful fuzzing often requires that malformed or unexpected data be inserted into quite specific areas of an applications input. This is because the program usually needs to perform some sort of processing on the user supplied data in order for an exploitable crash to be triggered, and this requires that we enter the fuzz values into areas of a network protocol where the application is expecting to find the right sort of input.
Data fields, size fields, command arguments, input strings and sometimes even commands themselves are all examples of the types of input that can be used to generate these types of errors.
This understanding of the network protocol can be gained in a number of ways — by reviewing RFC documents, by generating traffic using a client application and using a tool such as Wireshark or tcpdump to capture the result, or, for very simple protocols, you can just directly interact with the application to see how it works.
This is what we will do in the case of Vulnserver. So we can begin, we first we need to start it up. Since we are fuzzing Vulnserver and we want to see what is happening to it if we manage to cause an exception, we will run the program in a Debugger. Start up OllyDbg on your Windows system, and use it to open vulnserver. At this point, the program is running more or less as normal, however if we trigger a crash in the Vulnserver process, the debugger will take control and will allow us to see what is going on in the processors registers and the programs memory at the time of the crash.
Now, from our Linux fuzzing system, we can connect to the running instance of Vulnserver using netcat. We will run netcat in double verbose mode -vv in order to get some additional information about the connection, and we will disable DNS resolution -n. Enter HELP for help. The response we receive after connecting to Vulnserver tells us that we can enter HELP to obtain, some help.
Lets try that and see what happens:. Lets try entering some of these commands, as well as some other random strings, and see what happens. What about if we try it again, but this time with some generic text thrown in after the command. OK, commands look to be case sensitive. Now lets try another supported command, along with a random parameter. OK, that gave a different response as well. Now lets see if we can get more information about one of the supported commands. Considering this, some of the ways in which we could introduce fuzzed data into the application could be to insert it:.
This is an extremely simple example of protocol analysis, but I believe it demonstrates the general pre-fuzzing process fairly well — we determine how the program receives input data from the user, and use that method to insert fuzzed data into the application. In the previous section, we identified that it might be useful to send fuzzed strings in place of a supported command, and as parameters to supported commands that do, and do not seem to support parameters.
Lets start off with the simplest case first — sending a fuzzed string in place of a supported command. My target copy of Vulnserver is listening on a machine with the IP address The filter looks like the below — if you have your target system on a different IP address, or Vulnserver is listening on a different port adjust your filter accordingly.
If you leave it running, this SPIKE script should complete after a few minutes, and if you check VulnServer running in its debugger, you will notice that it seems to be running fine — there has been no crash. So it appears that just sending bad data in place of a supported command does not cause VulnServer to crash or at least sending the bad strings generated by SPIKE in place of a command does not cause Vulnserver to crash.
View code. Type "show copying" and "show warranty" for details. Type "show configuration" for configuration details. For help, type "help". Type "apropos word" to search for commands related to "word" Reading symbols from rot Disabling abstract command writes to CSRs. Breakpoint 1, main at rot View license. Releases 2 Version 1. Dec 17, Packages 0 No packages published. Spike messages are a clutter free zone- so message history is no longer added to your replies by default. Use collapsible lists in Notes to manage some serious projects, to do lists, or even write your trilogy with a zillion chapters.
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