A high-severity Electrum wallet bug let a malicious server swap users’ pending transactions and trick them into signing the theft themselves — and Electrum has confirmed the attack happened in the wild, with at least one case of stolen funds.
The flaw, documented in Electrum’s GitHub security advisory GHSA-6jp4-8v48-cc5v on Oct 24 and patched the same day in Electrum 4.8.3 (commit 90fe308), is a masterclass in social engineering dressed up as software: the victim’s own wallet displayed the attacker’s transaction, and the victim’s own click paid it out.
Table of Contents
How the rogue server swap works
- You broadcast a legitimate transaction. A compromised Electrum server swallows it instead of relaying it to Bitcoin.
- The server pushes a conflicting transaction into your wallet’s history, with the outputs quietly redirected to the attacker’s address.
- Electrum historically trusted its main server for displaying unconfirmed transactions — confirmed ones are validated locally via SPV — so the forged transaction renders as if it were yours, just stuck.
- Seeing a “stuck” payment, you do what any reasonable person does: you accelerate it with a replace-by-fee bump.
- The wallet signs the transaction it is showing you. The higher-fee version broadcasts — paying the attacker. Funds gone.
Notice what is missing from that list: no exploit kit, no remote code execution, no seed phrase exfiltrated. The bug is that the wallet signed what the screen showed without verifying the outputs — a trust gap between server and signature.
Confirmed in the wild
Electrum acknowledged malicious servers were already performing the attack and confirmed at least one case of stolen funds. No aggregate dollar loss has been disclosed — figures circulating alongside this story, including the $89 million to $130 million attributed to the separate Coldcard firmware entropy flaw, belong to a different incident entirely and should not be attached to this one.
The disclosure lands in a busy week for wallet security: yesterday we covered the Keystone breach that exposed customer data past its 180-day deletion promise, and the Ledger hardware implant probe remains on the watchlist. Hardware breaches hit your data; this one hits your coins directly.
The fix, and what to do now
Electrum 4.8.3 adds signature verification for unconfirmed transactions, so a server-substituted transaction can no longer display as legitimate. If you use Electrum:
- Upgrade to 4.8.3 immediately (binaries released Oct 24 for desktop and Android).
- Connect only to official or verified Electrum servers — never add a stranger’s custom server.
- Before approving any fee bump, confirm the receiving address on your signing device’s screen.
- Any pending “speed up” prompt whose outputs you cannot independently verify should be treated as hostile.
The wider lesson is one the industry keeps relearning: whatever displays a transaction is part of your trusted computing base. If the display can be lied to, the signature will happily confirm the lie.
Source: Electrum GitHub Security Advisory GHSA-6jp4-8v48-cc5v (Oct 24, 2026); Electrum 4.8.3 release notes; crypto.news coverage.
