Bitcoin wallet Electrum has disclosed a high-severity vulnerability actively exploited by malicious servers, resulting in confirmed user fund losses. The flaw affects all versions prior to 4.8.3 and allows attackers to intercept broadcast transactions and replace them with conflicting transactions directing funds to attacker addresses. If users apply Replace-By-Fee (RBF) to increase transaction fees, the compromised wallet signs and sends the funds directly to the attacker. Electrum confirmed that some servers have already executed this attack in the wild, with two users reporting related incidents. One victim lost funds after raising the fee on a manipulated transaction, though the specific amount remains undisclosed. The vulnerability was patched in version 4.8.3, released via GitHub security advisory. The official recommendation urges immediate upgrades to version 4.8.3. Until updated, users must carefully verify recipient addresses and amounts when signing any transaction, including fee bumps. Electrum clarified that users connecting exclusively to their own servers are not affected by this vulnerability.