SH1MMER

Shady Hardware 1nstrument Makes Machine Enrollment Retreat

Website, source tree, and write-up for a ChromeOS:tm: enrollment jailbreak

The Fog....

Downgrading and unenrollment has been patched by Google:tm:. If your Chromebook has never updated to version 112 (or newer) before (check in chrome://version), then you can ignore this and follow the normal instructions. If not, unenrollment will not work as normal.

Fog Bypass Details

If your Chromebook is on version 112 or 113, unenrollment is still possible if you're willing to disable hardware write protection. On most devices, this will require you to take off the back of the Chromebook and unplug the battery, or jump two pins. Further instructions are on the website.

"Unenrollment" Without Disabling Hardware Write Protection

If you aren't willing to take apart your Chromebook to unenroll, you can use an affiliated project, E-Halcyon to boot into a deprovisioned environment temporarily. This will bypass both issues of The Fog and The Tsunami, however further caveats are listed on the website.

The Tsunami

Disabling write protection has also been patched by Google:tm:. If your Chromebook has never updated to version 114 (or newer) before (check in chrome://version), then you can ignore this and follow the Unpatch instructions. If not, disabling write protection will not work as normal.

Tsunami Bypass Details

If your Chromebook is on version 114 or newer, unenrollment is still possible by bridging two pins on the firmware chip On most devices, this will require you to take off the back of the Chromebook and then use a piece of tinfoil, wire, or other conductive material to bridge the two pins. Instructions are not listed and this solution is not recommended as you risk damaging the Chromebook.

If you are aware of the risk and are still willing to perform this, be aware that you must bridge the WP and VCC pins, NOT WP and GND, despite what the blog post says. Look up the model of your chip online, most will be 8/16/32 MB (64/128/256 Mb). Find the pinout for WP and VCC. Most will use pins 3 and 8 respectively.

What is SH1MMER?

SH1MMER is an exploit found in the ChromeOS shim kernel that utilitzes modified RMA factory shims to gain code execution at recovery.
For more info, check out the blog post/writeup here

How does it work?

RMA shims are a factory tool allowing certain authorization functions to be signed, but only the KERNEL partitions are checked for signatures by the firmware. We can edit the other partitions to our will as long as we remove the forced readonly bit on them.

How do I use it?

The prebuilt binaries have been taken off of the official mirror (dl.sh1mmer.me), so you'll have to build it from source.

Here's how you do that. First, you need to know your Chromebook's board. Go to chrome://version on your Chromebook and copy the word after stable-channel. If chrome://version is blocked, you can search up your Chromebook's model name on chrome100 and see what board it corresponds to. DO NOT DOWNLOAD A RECOVERY IMAGE FROM chrome100, IT WILL NOT WORK.

If your board name is in the list below, great! Find the RAW RMA shim corresponding to your board online. We can no longer provide raw RMA shims due to legal reasons. More information

(A-B) ambassador, brask, brya
(C) clapper, coral, corsola
(D-E) dedede, enguarde
(G) glimmer, grunt
(H) hana, hatch
(J-N) jacuzzi, kukui, lulu, nami
(O) octopus, orco
(P-R) pyro, reks
(S) sentry, stout, strongbad
(T-Z) tidus, ultima, volteer, zork

If it's not, good luck. You'll have to try and call up your OEM and demand the files from them, which they are most unlikely to give to you.

Building A Beautiful World Shim

IMPORTANT!!!! IF YOU HAVE EITHER THE coral OR hana BOARDS, OR SOME OTHER OLDER BOARDS (which?), DO NOT FOLLOW THESE INSTRUCTIONS, INSTEAD SKIP TO THE "Building A Legacy Shim" SECTION

Now we can start building. Type out all of these commands in the terminal. You need to be on Linux or WSL2 and have the following packages installed: git, wget. Note that WSL doesn't work for some people, and if you have trouble building it it's recommended to just use a VM or the web builder. THE WEB BUILDER DOES NOT INCLUDE PAYLOADS!! YOU MUST BUILD IT MANUALLY FROM SOURCE FOR PAYLOADS

git clone https://github.com/MercuryWorkshop/sh1mmer
cd sh1mmer/wax
wget https://dl.sh1mmer.me/build-tools/chromebrew/chromebrew.tar.gz
sudo bash wax.sh path/to/the/shim/you/downloaded.bin

When this finishes, the bin file in the path you provided will have been converted into a SH1MMER image. Note that this is a destructive operation, you will need to redownload a fresh shim to try again if it fails.

If you want to build a devshim, replace chromebrew.tar.gz with chromebrew-dev.tar.gz and add --dev to the end of sudo sh wax.sh /path/to/the/shim/you/downloaded.bin Devshim builds will mount a much larger Chromebrew partition over /usr/local, allowing you to access a desktop environment and even FireFox from within SH1MMER. It's what allowed us to run doom on a shim.

After injecting, you may continue to the "Booting Into A Shim" section.

Building A Legacy Shim

The raw shim files for boards such as HANA or CORAL were built before graphics support was added into the tty. This makes it impossible for the Beautiful World GUI to work and thus a legacy CLI-only shim must be built.

Type out all of these commands in the terminal. You need to be on linux and have the following packages installed: git, wget, gdisk, e2fsprogs.

Note that the legacy shim will work on all boards. The legacy version of wax now supports nano (shrunken) shims!

git clone https://github.com/MercuryWorkshop/sh1mmer
cd sh1mmer/wax
sudo bash wax_legacy.sh -i path/to/the/shim/you/downloaded.bin

After injecting, you may continue to the "Booting Into A Shim" section.

Booting Into A Shim

Once you have injected your raw shim with SH1MMER, go into the Chromebook Recovery Utility, select the settings icon (⚙️), select Use local image, and then select your injected shim. Alternatively, you can also use other flashers such as BalenaEtcher, Rufus, UNetbootin, and etc. This may take up to 10 minutes, depending on the size of your shim and speed of your USB drive.

On the Chromebook, press ESC + Refresh (↻) + Power (⏻) at the same time to enter the recovery screen, then press CTRL + D at the same time and press Enter. This should enable Developer Mode or turn off OS Verification. This may be blocked by system policy, but that doesn't matter.

Press ESC + Refresh (↻) + Power (⏻) at the same time again, then plug in your USB with SH1MMER and you should be booting into the Beautiful World GUI or a CLI screen. From here, you can play around with the options and do what you want.

Credits

CoolElectronics - Pioneering this wild exploit
ULTRA BLUE#1850 - Testing & discovering how to disable rootfs verification
Unciaur - Found the inital RMA shim
TheMemeSniper - Testing
Rafflesia - Hosting files
generic - Hosting alternative file mirror & crypto miner (troll emoji)
Bypassi - Helped with the website
r58Playz - Helped us set parts of the shim & made the initial GUI script
OlyB - Scraped additional shims
Sharp_Jack - Created wax & compiled the first shims
ember#0377 - Helped with the website
Mark - Technical Understanding and Advisory into the ChromeOS ecosystem

sealsrock12 / sh1mmer