The firmware for Trezor Safe 3, 5, and 7 has a confirmation‑binding flaw in the Ethereum sign_tx / sign_tx_eip1559 flow. During contract interaction the device verifies only the first chunk of calldata shown on its display; however, the signature is generated over the entire streamed calldata. An attacker can trick a user into accepting a displayed command and then supply a different tail of calldata that alters the signed transaction. This permits an attacker to modify the intent of a transaction after the user believes it is safe, thereby compromising both integrity and authenticity of Ethereum transactions made with the device.

Affected vendors: Trezor. Products impacted are Trezor Safe 3, Trezor Safe 5, and Trezor Safe 7 firmware. Version details are not specified in the advisory, but any firmware build lacking the 70c9b0c fix is susceptible.

The CVSS score of 5.9 indicates moderate severity, and the EPSS score of less than 1% suggests a low likelihood of exploitation at present. The vulnerability is not listed in CISA KEV. Exfiltration likely requires physical proximity or user cooperation, as the attacker must provide new calldata to the device after the initial confirmation. The flaw can be exploited by anyone who can supply a malicious payload to the device and convince a user to authorize it, leading to unauthorized or altered transaction signing.