Trezor has increased its optional wallet passphrase limit from 50 to 128 characters in its October software update, citing the July 2026 Coldcard attacks that exposed Bitcoin recovery phrases and led to large-scale thefts.
The change was announced on November 1 and applies to Trezor Model T, Safe 3, Safe 5, and Safe 7 devices after a firmware update. The older Model One remains capped at 50 characters. Trezor said longer passphrases give experienced users another layer of protection if their recovery phrase is exposed.
According to Trezor, a passphrase is separate from a recovery phrase and creates a different wallet with different addresses and balances. Unlike an account password, it cannot be reset or recovered. A mistyped passphrase opens another wallet, which may appear empty even when the original still holds funds. Trezor recommends recording passphrases securely and testing access before transferring assets.
The update follows the July 2026 Coldcard vulnerability. Trezor said the issue was disclosed on July 30, but researchers later traced the flawed code to a commit from March 1, 2021. The regression allowed some Coldcard devices to generate recovery seeds with far less randomness than intended: about 40 bits for Mk3 and about 72 bits for Mk4, Mk5, and Q devices, down from about 128 bits. Attackers could enumerate candidate seeds and derive addresses without physical access.
On July 31, about 594 BTC, worth roughly $38 million, was stolen from around 500 wallets in 25 minutes. By August 12, estimates put losses at roughly $116 million across more than 5,200 addresses. Some Coldcard users avoided immediate losses because their wallets required an additional passphrase that attackers could not reconstruct.
Trezor also acknowledged that the longer passphrase cap does not automatically increase security. BIP-39 derivation uses PBKDF2-HMAC-SHA512 with only 2,048 iterations, so once a seed is known, testing candidate passphrases is cheap. The real protection comes from the passphrase's randomness, not its length. A 128-character human-memorable phrase can carry less entropy than 20 random characters from a generator.
Coldcard maker Coinkite released corrected firmware versions 4.2.0 for Mk2/Mk3, 5.6.0 for Mk4/Mk5, and 1.5.0Q for Q, but these do not repair already generated weak seeds.
Separately, on October 30, Trezor warned customers about a suspected hardware implant in a Safe 5 device purchased through former reseller CryptoBilis. Trezor said it had reviewed photographs and interviewed the customer but had not physically examined the device, and no confirmed losses were reported. Customers who bought from CryptoBilis from March 2026 onward were advised to move funds to new wallets with fresh recovery phrases.
