LinkLiar VS VW_Flash

Ever since I used https://github.com/halo/LinkLiar , my Mac disconnects and reconnects from WiFi every few minutes. I have tried resetting network preferences and nothing has worked.

Are you on Mac, Windows, Linux, or something else? If you're on Mac, there's an open source app I use. If you're on Windows, there are some tutorials you can follow to do it without installing anything (I've tried it on Windows once a long time ago, so I'm not really sure if it still works). If you're on Linux, there are also tutorials, though I've never tried them before so I'm not sure if they work. Also, to avoid suspicion, you may want to change your netBIOS/localhost name (actually, I'm not sure if they're the same thing, but changing either seems to have the same result since its visible when logged into your router settings. You can do it via Settings or Terminal for Mac and there are probably some tutorials for Windows and Linux.)

I did find an older VW "emergency start" product that claims to only work with Bosch MED17 and MED9, and I suspect it's using a memory-access primitive (either UDS or CCP) to release the immobilizer.

It's trivial to disable an immobilizer in software by re-flashing the ECU, yes, but modern ECUs have two strong protections against this:

* Cryptographic signature checking against update/re-flash payloads (I've done extensive research on these on VW Continental ECUs - https://github.com/bri3d/VW_Flash )

and an even better and more obvious protection:

* The ECU application software won't descend into the re-flash software (Customer Bootloader) unless the immobilizer is free (a valid key is present).

This is a lot of what helps to reduce surface area from an "emergency start" style attack to an AKL attack - now that the Customer Bootloader won't start without the Immobilizer being unlocked, an attacker needs to remove the control unit to flash it with a Supplier Bootloader exploit ( https://github.com/bri3d/simos18_sboot ) or physical access (BDM/JTAG).

This year I don't anticipate having much free time, so I'm trying to engage more contributors in side projects,

* Automotive ECU tooling, https://github.com/bri3d/VW_Flash

* DJI FPV forward/reverse/all sorts engineering, https://github.com/fpv-wtf

I've been working a lot with various folks using Discord and contributions are gradually shifting from me towards others, which has been great to see. As the old adage goes, teaching a project is truly the final form of knowing one - much harder than hacking alone, but ultimately more fulfilling.

When I started my automotive ECU journey my goal was to demystify the "tuning" scene for a broader software engineering community, and I think I've generally been successful at this.

This week, as most weeks, I split my time outside of the day job and my other hobbies and obligations between Discord collaboration, Ghidra, and VSCode:

https://github.com/bri3d/VW_Flash - Flashing tools for select control modules in VW MQB and now PQ35 platform cars. This week I'm working on old stuff: a simpler exploit chain for older Simos ECUs, as well as tweaks to expand support to older DSG control units used in PQ35 platform vehicles.

https://github.com/fpv-wtf/msp-osd - I pushed a rearchitect of this on-screen-display overlay system for DJI FPV Goggles last week that seems to have sorted out a lot of issues - I switched from just passing through the OSD drawing messages from the Flight Controller to a system where the video transmitter maintains the OSD character buffer and sends a compressed representation of the screen state. This makes the system much more robust to packet loss in situations where the Flight Controller sends delta updates rather than frame-at-a-time.

I only really started publishing Open Source projects a year or two ago, and while they're pretty much my worst code by any objective measure, I've met some great people and really enjoy working on these. It's fun making things that achieve a goal without so much pressure of deadlines, stakeholders, and competing priorities.

VW_Flash: https://github.com/bri3d/VW_Flash/blob/master/docs/docs.md . Modern UDS control unit flashing: Preconditions RemoteRoutine, Programming Session, SA2 Seed/Key, Workshop Identifier, RequestDownload, TransferData, ExitTransfer, Checksum RemoteRoutine, rinse and repeat. Pretty much the same for any UDS control unit. Other manufacturers have some little tweaks to the Preconditions and Workshop Identifier, but conceptually this is how UDS flashing works overall. Also contains examples of modern control unit encryption (rolling cipher for Temic DQ250, crappy XOR for Simos8, AES for Simos12 and up and DQ381) and checksums (mostly CRC based, some header-defined, some not). Crash course in SBOOT/CBOOT/ASW/CAL layout of modern control units.

That's pretty cool! I wonder how properly they were really signed - there are _so many_ mistakes even in systems that at least don't use an example key off the Internet.

The most common ones I know of are:

* Out-of-bounds write issues allowing "signature was validated" flags to be overwritten in Flash memory, like https://github.com/jglim/UnsignedFlash

* State machine mistakes, like https://github.com/bri3d/VW_Flash/blob/master/docs/docs.md - allowing Flash to be written again after it was already written, without an erase first.

* Filesystem parsing mistakes, like those in a number of VW AG head units: https://github.com/jilleb/mib2-toolbox/issues/122

* The use of RSA with E=3 and inadequate padding validation, like https://words.filippo.io/bleichenbacher-06-signature-forgery... .

* Failure to understand the system boundaries, like in the second part of https://github.com/bri3d/simos18_sboot where "secret" data can be recovered by halting the system during a checksum process.

* Hardware fault injection issues, as used in https://fahrplan.events.ccc.de/congress/2015/Fahrplan/system... .

Fundamentally this is of course, a very hard problem, since in the "protect against firmware modification" case, the attacker has physical access. But, compared to the state of the art in mobile devices and game consoles, automotive stuff is still way behind.

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No, this EPS control module is remarkably primitive even by late 2000s standards and several generations behind today's state of the art.

More modern control modules with a bit more resource available to them will use AES as the symmetric encryption (although there are also fixed-key XOR schemes and custom stuff used like this: https://github.com/bri3d/VW_Flash/blob/master/lib/decryptdsg... ).

The keys and even IV are usually fixed across a "model line" of ECUs, so once a decrypted flash memory can be extracted, this isn't much of a protection measure, but it's a lot better than XOR.

Then, in more modern control units, flash areas are also usually protected by both a checksum (usually some CRC permutation, although cute tweaks and random nonsense are common here too) and some form of digital signature.

I have been reverse engineering automotive ECUs for a while now - https://github.com/bri3d/VW_Flash . It's a nice change from my day job in enterprise engineering management, and I've met some fun people and taught several folks a lot of new concepts, which is always extremely rewarding.

My latest project has been reverse engineering the data-flash encryption in Simos18 ECUs. After some work, it oddly appears the encryption algorithm used is Mifare Hitag2. I'm hoping to be able to re-encrypt NVRAM channels soon, although the overall data flash "filesystem" / channel-system layout needs some more work before I am ready to release my findings.

3) For highly specialized applications, additional hardware is necessary. For example, on modern ECUs, often read/write access via diagnostic protocol is secured via encryption and signature validation, so to flash custom firmware requires a bypass of these measures. Sometimes this bypass can be via a vulnerability in the diagnostic protocol requiring no additional hardware, like on VW Simos18 , but other times the bypass requires manipulating the control unit beyond what the diagnostic port allows - custom serial protocol, specific sequences of GPIO manipulation, or PWM signals applied to specific pins.