Bitcoin wallet bug let rogue servers steal funds when users tried to speed up payments

A bitcoin wallet security flaw allowed malicious servers to trick users into signing payments to attackers when they tried to speed up transactions, with developers confirming at least one case in which money was stolen. Electrum, one of Bitcoin's oldest software wallets, disclosed the vulnerability on Saturday, saying some servers were already exploiting it. The developers received two reports in October, including one from a user who lost funds after approving what appeared to be a routine transaction-fee increase. The attack exploited how Electrum handles bitcoin payments that have not yet been confirmed by the network. Unlike a full Bitcoin node, Electrum relies on outside servers to retrieve transaction histories and broadcast payments.

First reported by CoinDesk. This page is a short excerpt; the full text is theirs.