Electrum Patches High-Risk Exploit: Upgrade to 4.8.3 Now — Malicious Servers Were Tricking Users Into Signing Stolen Payments
Electrum has released version 4.8.3 to fix a high-severity vulnerability that was already being exploited in the wild.
Versions before 4.8.3 trusted the main Electrum server for unconfirmed (mempool) transactions. A malicious server could intercept a newly broadcast transaction, suppress it, and insert a conflicting fake transaction into the wallet’s history that redirected the outputs to an attacker-controlled address. The fake transaction carried invalid signatures, but older clients did not verify those signatures on the user’s own inputs before displaying it as unconfirmed.
If the user then manually increased the fee via Replace-by-Fee (RBF), the wallet would sign the altered transaction — sending the funds to the attacker. In the reported cases, attackers crafted lookalike addresses that matched the last four characters of the intended recipient, exploiting the common habit of only checking the ending.
Electrum confirmed two incident reports, including one in which a user lost funds after bumping the fee. The fix in 4.8.3 now verifies signatures on wallet-owned inputs for mempool transactions before adding them to local history.
Users on any version prior to 4.8.3 should upgrade immediately from the official site (electrum.org) and verify the GPG signatures. Clients connected to fully trusted servers (for example, a self-hosted one) were not affected by this specific attack. As a general practice, always double-check the full destination addresses and amounts before signing any transaction, including fee bumps.
Self-custody remains powerful, but it still requires staying current with security patches.
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