Executive brief
Trezor Safe hardware wallets, which are used to securely store and manage cryptocurrency, are affected by a flaw in how they process Ethereum transactions. When interacting with smart contracts, the device may only show the user a portion of the transaction data for confirmation, while the final signature applies to the entire data set. This could allow a malicious actor to trick a user into signing a transaction that performs a different action than what was displayed on the device screen, potentially leading to unauthorized transfers or loss of funds.
Technical details
A confirmation-binding vulnerability exists in the Trezor Safe 3, 5, and 7 firmware within the Ethereum sign_tx and sign_tx_eip1559 flows. The root cause is an improperly implemented security check (CWE-358) where the device confirms only the initial calldata chunk to the user, but the cryptographic signature commits to the full streamed calldata. An attacker can exploit this by presenting benign calldata for user confirmation and then supplying a malicious 'tail' to the streamed data that alters the transaction's effect. This requires the attacker to influence the transaction data sent to the device, typically via a compromised or malicious decentralized application (dApp) interface. The issue is fixed in firmware commit 70c9b0c.
Affected products
- Trezor Safe 3 Before commit 70c9b0c
- Trezor Safe 5 Before commit 70c9b0c
- Trezor Safe 7 Before commit 70c9b0c
Timeline
- 2026-02-14: other: Fix authored
- 2026-03-19: patched: Fix committed to repository
- 2026-07-21: advisory: CVE published