I went through Mark Karpeles' teardown of a Ledger Flex that a buyer named Ben York picked up at a Metapod shop inside Singapore airport, and the extra circuit board folded under the screen is the part that should worry anyone who owns a hardware wallet. The main board looked normal. Someone had opened the case, added a small board of their own and wired it into the display, so the wallet could show a fresh seed phrase to its new owner while a second chip copied it. The device booted and behaved like a Flex.
What the teardown found
The first sign was physical. Around the notch in the casing there were marks that looked like someone had pried the case open before. Ledger glues the back panel down, so the case comes off with pry tools worked around the perimeter. A heat gun would normally soften the adhesive, but firm prying gets the cover loose, and the marks left behind are the kind of thing a careful buyer might spot before ever plugging the device in.
Under the cover sat an extra board, labeled version 1.2, that does not belong in a factory unit. The radio antenna unplugs easily, which makes the back cover simple to detach, and the bottom colored trim came off with difficulty because whoever opened the device had re-glued it. A factory unit does not need fresh glue, and a trim piece that fights back is a sign that someone has been inside before.
A factory-sealed Ledger Flex, opened for comparison, settles it. The authentic device has a clean backplate and a larger battery. The compromised one has custom wiring, an altered display connector and a smaller cell. The main board underneath still carries the parts you would expect, including the secure element and the Nordic microcontroller. The attack lived entirely in the added hardware, which is why the wallet still powered on and ran its normal setup.
The device powered on by accident during the disassembly, so the internal battery gets disconnected for safety and the metal shielding comes off to show the layout and the power routing. That is where the custom wiring becomes obvious: the implant is not sitting loose inside the case, it is connected into the device's own circuits.
How the implant read the seed phrase
The implant did not need to break encryption. It sat on the display bus.
A custom ribbon cable intercepts the connection between the main board and the screen. The same adapter splits power from the battery terminals, so the rogue board starts at the same moment as the wallet. Folded beneath the lower frame, it sees everything the screen shows: the recovery phrase during setup, the PIN as it is typed, and any address or amount the owner confirms before signing.
The rogue board itself is a rigid, high-density printed circuit board with test points, an STM32 microcontroller and dedicated memory. Karpeles calls it a sophisticated, professionally manufactured interceptor, not a hand-soldered hobby project. Someone designed a board to fit a specific model, sourced the parts and built a production run. The implant transmits the seed the device generates on initialization, so any asset deposited on the wallet can be taken by the attacker.
A seed phrase is the master secret of a crypto wallet: a list of words, usually 12 or 24, that can restore the wallet on any compatible device. Anyone who has it controls the funds, with or without the original hardware. A PIN protects the device in your pocket, but it does not help if the phrase was copied the moment the device generated it. The implant captured both the phrase and the PIN entry, which removes every layer at once.
What a Ledger Flex is meant to do
A hardware wallet is a small computer that keeps private keys away from your phone and laptop. Instead of signing transactions on a machine that is online all day, you connect the device, check the details on its own screen and approve with its buttons. The private key stays inside. That is why people store large amounts on devices like this.
The Flex is one of Ledger's touchscreen models. The screen greets the owner with "Welcome to Ledger Flex your digital signer", and the back cover carries the model marking LFLX-ORANGE and FCC ID 2ACZT-LFLX. Inside, the secure element is the chip built to hold secrets and resist extraction, and the Nordic microcontroller handles the rest of the device's work. A secure element raises the cost of pulling keys out of a stolen device, and it is the reason a hardware wallet is generally safer than a phone app for a large balance.
The teardown does not cover the Flex's price, the coins and networks it supports, the setup steps or its firmware source code, so check those with Ledger before you buy.
A secure element protects the keys once they are inside. It cannot protect a phrase that is displayed on a screen someone else is reading. The same goes for the PIN: the chip can rate-limit guesses, but it cannot hide a number that is typed on a screen with a tap on the wire behind it. The implant did not need to defeat the secure element, the firmware signature checks or any cryptographic protection. It only needed to watch the wire that feeds the screen.
The physical clues that gave it away
Most of the evidence was visible before the case came off. Pry marks near the notch, a trim piece that had been re-glued, and a battery that did not match the factory part. The table below sets the two units side by side.
| Part | Factory unit | Compromised unit | | Battery | 200 mAh | 160 mAh | | Backplate | clean | custom wiring | | Display connector | standard | altered, with adapter cable | | Extra board | none | version 1.2 board with STM32 chip and memory |
Dropping from 200 mAh to 160 mAh frees a few millimeters of depth, and that is where the implant sits. A buyer who never opens the case would not notice the difference in capacity, and the device still powers on and runs. The attacker traded battery life for space, and the loss is small enough that most people would never question it.
The packaging can look fine, the screen can light up, and the setup can run exactly as expected. The tampering shows up in the seams, the glue and the parts that do not match. If you ever do open a device, or see photos of one that has been opened, those are the details to compare.
Why the screen is the place to attack
Every hardware wallet has to show you the recovery phrase at least once, because you have to write it down. That moment is the weakest point in the whole flow, and it is a physical one. The phrase has to travel from the secure element to the display, and anything sitting on that path sees it in the clear.
A user should never generate a seed on a device of unknown history, and that is true. But the setup flow is designed to be followed, and a new buyer has no reason to suspect the screen. The attack works because it targets the one moment when the secret must be visible.
It also assumes the attacker can get physical access to the device before the buyer does. In this case, the unit was bought from a retail shop inside an airport, which is exactly the kind of place where stock passes through several hands. There had been no prior evidence of altered units sold at airport retail, so this looks like a single confirmed case rather than a known pattern. One case is enough to change how you buy, though.
What this says about supply-chain attacks
A supply-chain attack happens when someone interferes with a product before it reaches you. In crypto, the usual version is a fake app or a tampered download. This is the physical version: a real device, opened, modified and put back on a shelf.
Buy from the maker or an authorised seller, not from a marketplace listing or a stranger. Check the packaging for signs of resealing. Look at the seams and the notch for pry marks. If the device arrives already set up, or asks you to restore a phrase you did not create, stop. A new device should generate a new seed during setup, and you should be the one writing it down.
Tamper-evident packaging helps, but it is not a guarantee. A determined attacker can reproduce a box, and a retail return can end up back on a shelf. That is why the habits matter more than any single check: buy direct when you can, inspect what arrives, and treat any doubt as a reason to start over with a device you trust.
Karpeles' advice is blunt: "If your hardware wallet ever shows signs of prior opening or altered packaging, assume it is completely compromised. Any seed phrase generated on it must be abandoned immediately."
What to do if you suspect your device was opened
If you have any doubt about a device's history, treat the seed on it as burned. Do not keep using it because the balance looks fine. The attacker does not need to move funds on day one; a copied seed can sit unused for months, and the first sign of trouble may be a balance that disappears while the device is in a drawer.
- Stop using the device and do not enter your PIN again.
- Create a new wallet on a device you trust, bought from the maker or an authorised seller.
- Write the new recovery phrase on paper and keep it offline.
- Move your funds to the new wallet and confirm the transaction on the new screen.
- Retire the old device and, if you can, report the seller.
Never type a seed phrase into a website, a chat window or a support form. No legitimate support person needs it, and any page that asks for it is trying to take your funds. The same goes for photographing it or storing it in a password manager on a connected computer. A seed phrase is the wallet, so anyone who sees it can spend from it.
If you are setting up any hardware wallet for the first time, start with a small amount. Send a test transaction, confirm it arrives, and only then move the rest. That habit catches mistakes before they are expensive, and it gives you a reason to check the address on the device screen, which is the habit the whole design depends on.
How I would judge a hardware wallet after this
The Flex is still a hardware wallet with a secure element and a screen that lets you check what you sign. Nothing in the teardown suggests the design is broken. What it shows is that the security of the device depends on the chain of custody before it reaches you, and that chain is only as strong as the shop, the warehouse and the courier.
So I would judge any hardware wallet on two things. First, the parts you can verify: does the maker sell direct, is the packaging tamper-evident, and does the setup force a new seed? Second, the parts you cannot: who handled the box, and would you notice if they had opened it? A device that passes every software check can still fail the second question.
Hardware wallets remain the safer place for large holdings than a phone app, as long as the device is genuine. A factory Flex has a 200 mAh battery. The compromised unit had a 160 mAh cell to make room for the implant. You will not open your own device to check, and you should not have to. But if the case shows pry marks or the trim looks re-glued, stop and start again with a device you bought from a source you trust.
