Ledger altcoin apps could sign Bitcoin transactions (app isolation bypass)

Ledger’s bulletin LSB-014 states that the Bitcoin app and most of its derivatives on the Nano S and Nano X did not enforce the restriction that each app derives keys only on its own path. As a result, a Bitcoin derivative app could derive public keys or sign Bitcoin transactions. The bulletin lists Litecoin, Dogecoin, Dash, Bitcoin Testnet and other derivative apps as affected; Bitcoin Cash, Zcash and some others were not, because they use a different signature format.

According to the researcher, as reported by Cointelegraph, a user could be shown a transaction for a less valuable coin, such as Litecoin or a Bitcoin fork, while a real Bitcoin transaction was released; the Bitcoin Testnet app would also accept mainnet Bitcoin transactions and display them as testnet. An attacker needs to get the user to approve such a transaction prepared by malicious software on the host.

The researcher monokh reported the issue through Ledger’s bug bounty programme on 2 May 2020, and a 90-day disclosure date of 2 August was agreed. Ledger states the researcher published details on 4 August without first notifying its security team, and that it updated the Bitcoin app on 5 August. Ledger says it did not block unusual paths because that could lock users out of their funds; instead Bitcoin app 1.4.6 shows a warning when a derivative app derives on an unusual path. The researcher said, according to Cointelegraph, that Ledger had not fully fixed the issue and had chosen a warning over a complete fix.

What Ledger advises:

• Update the Bitcoin app to version 1.4.6 or later.