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UDS Simulator and Fuzzer

Unified Diagnostic Services Simulator

The UDSim is a graphical simulator that can emulate different modules in a vehicle and respond to UDS request. It was designed as a training tool to run alongside of ICSim. It also has some unqiue learning features and can even be used to security test dealership or other tools that plug into the OBD dongle

NOTE: This is a complete rewrite of uds-server.

alt text


UDSim takes the following command line options:

  Usage: udsim [options] <can-if>
     -c <config file>    Configuration file for simulator
     -l <logfile>        Parse candump log to generate learning DB
     -f                  Fullscreen
     -v                  Increase verbosity

The only required argument is the CAN interface. There are some example CAN initialization scripts in the src folder for setting up canX and vcanX interfaces if you need them.

UDSim as three modes: Learning, Simulation and Attack


By default UDSim listens for activity on the specified CAN interface and will automatically learn UDS capable modules in the vehicle based on live network traffic. To gather data you should attach a diagnostic device of some sort and run it against your vehicle while UDSim is monitoring the CANbus.

Press the disk icon to Save the learned information. When you press Save a config file called, config_data.cfg is created. This is a fairly easy to read the summary of UDS Can packets layed out in an INI format. You may want to copy this file and give it a specific name once you saved it so you don't accidently overwrite it. This file can be used later by passing the -c option to UDSim.

You can get UDSim to learn from recorded network traffic as well. If you feed UDSim a logfile via the -l option, it will parse all of the logging information and then automatically switch to simulation mode once it is done. The logfiles are in candump format.

Because UDSim uses network communication to learn about modules in the vehicle that can communicate to UDS it does not need any previous knowledge of the vehicle to work. It can work on any vehicle that uses ISO-TP. It has some base knowledge of common UDS but does not rely on it and should work even on new vehicles or with vehicles with non-standard UDS commands.


Once you are satisfied with that UDSim has learned enough informaion you can press the MODE button to toggle the state to Simulation. At this point UDSim will simulate the vehicle. You can detach UDSim from the actual car and your diagnostic tools should still function and pull informaion as if you were attached to a real car.

Note for presenters: UDSim works very well for demonstrating attacks without showing the vehicle or device directly. You can record your attack session with UDSim (or any CAN Logger) an once UDSim has monitored the traffic you can save and modify the config file to protect the guilty. Then all you need to bring with you on stage is UDSim and the config file and you can recreate the attack in a live interactive manner.

Simulation is also good for testing out CAN related tools or providing classes. Please note that simulation mode (in it's current revision) won't make up traffic it has never seen. So don't expect to query information in simulation mode that you it hasn't seen traffic for.

Simulation Options

There are two options available on a modules info card: Fake Responses and Ignore. Ignore is fairly self explanatory. If you set a module to ignore then it will not respond to incoming requests.

Fake Responses uses behavior simular to uds-server in that it will try to create a response to any request even if it hasn't learned how that request works (ie: never seen it before). It does this by using the standard UDS syntax for responses and it will just plug in some default or random values for a response. This is mainly only useful to see what a tool is trying to talk to or if you need a module to use a mix of learned behavior and simulate behavior for any missing UDS requests.


UDSim has a builtin fuzzer. This is a very limited fuzzing system compared to a full blown fuzzing framework. However it can be useful for quick and easy fuzzing of a device and it understands and respects the ISO-TP protocol (unless you don't want it too).

Attack Options

The module info card has two options: Fuzz VIN and a Fuzz Level.

When you are doing fuzzing of a module, it is often good to keep the VIN the VIN from changing. Many automototive tools use just the VIN to decide that they are indeed talking to the expected car. So unless you are testing the VIN inputs of the diagnostic tools, it is usually best to leave this unchecked.

Fuzz Level. When the bar is to the far left that disables fuzzing and makes the module work in simulation mode. This can be useful if you want some modules to fuzz while others to work properly. This bar was originally designed to work with the fuzzing levels of uds-server but we are currently re-evaluating the fuzzing plan. As it stands here are the levels:

  • 0 - No Fuzzing, simulation on
  • 1 - Fuzz the data portion of a responses
  • 2 - TBD - Current plan, variable length fuzzing
  • 3 - TBD
  • 4 - TBD - Current plan, fuzz even ISO-TP, complete random

For now just use fuzz level 1 or 0. Most likely we will implement level 2 as planned and if there are better ideas for 3 and 4, let us know. For more complex fuzzing you should use Peach Fuzzer.

Peach Fuzzer

During the original design of UDSim it was going to use a built-in fuzzing system much like the uds-server predecessor. However, it was later decided that it would be better to offload fuzzing to a more complete engine. For this reason we have decided to export the learned information to another open source utility, Peach Fuzzer. There are still widgets in the UI for fuzzing that currently do not do anything. This is because we are still deciding if this is the correct approach. We may use the slider to change how Peach is fuzzing or we may scrap Peach altogether.

The purpose of UDSim attack mode is to fuzz responses from the (simulated) vehicle. This is very useful in testing for vulnerabilities in dealership tools and in security auditing tools. We want to make UDSim easy to use but also allow the flexibility a research will need to dive in deeper in their research.

Peach XML files are saved to fuzz_can.xml and can be further modified for your own testing purposes.

For now consider the Attack mode very alpha.

NOTE: There is currently a bug with Mono for the CAN publisher. In the mono source for UnixSocket, Mono has a feature that can check if the socket is writable. It does this by writing a 0 byte frame to the socket. This causes an error on a CAN socket which in turn makes Mono mark the socket as unwritable by setting a flag. Even if you later send a valid frame length, Mono will not even try to write the packet because of this flag.

Issue is here:

			long write = Native.Syscall.write (fileDescriptor, IntPtr.Zero, 0);
			if (write != -1)
				canWrite = true; 

There are a few ways to work around this. We can wriate a different publisher that uses socketcand or a even more hacked up version that calls out to can-utils.

I'm looking for some peach fuzzing experts to pitch in some feedback on the best direction to go with this. Until this the fuzz_can.xml is in a hold state until we know what type of data would be easiest for the publisher to digest.


You need libsdl2-dev, libsdl2-image and libsdl2-ttf

For Attack Fuzzing

The goal of UDSim is to offload the fuzzing to an actual fuzzing engine. The Peach Fuzzer was selected as a good open source engine for fuzzing.

The Community version can be obtained here:

You will need to copy the folders in UDSim to the source of Peach

  cp Peach.Core.OS.Linux/Publishers/* <your peach source folder>/Peach.Core.OS.Linux/Publishers/

In the peach folder you will then want to compile a new version of peach:

  ./waf install --variant=linux_x86_64_debug

Note at the time of this writing there was a bug where you also needed to delete the file: Peach.Core.Analysis.Pin.BasicBlocks/wscript_build to get peach to compile on 64 bit linux.

Once you have compiled then put a peach script in your path. UDSim assumes peach is in the search path.

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