A fee-bump trick can make older versions sign a payment to an attacker. Here's who's at risk, what to do right now, and what Electrum says is safe.
🚨 If you use Electrum, this one is worth five minutes today. A flaw in older versions is already being used to steal Bitcoin.
Electrum released version 4.8.3 on October 24 and called it a critical security fix. Every version before 4.8.3 is affected.
🔍 Here's how the attack works.
When you bump a transaction fee using Replace-by-Fee, a malicious server can intercept your transaction and show a fake one in your wallet history that sends $BTC to the attacker's address. Your wallet can then sign it as part of the fee increase. Electrum has confirmed two incident reports, including one where user lost funds. The fake addresses even matched the last four characters of the real recipient, so a quick glance won't catch them.
✅ Who's at risk, and who isn't.
If you're on a version before 4.8.3 and connect through servers you don't control, you're exposed. Electrum says clients connected to trusted servers, such as your own, aren't affected by this attack.
🛠️ What to do right now
Update to 4.8.3 or later and download it only from electrum.org. Check the GPG signature before installing.
If you can't update yet, check the full destination address and amount every time you sign, including fee increases.
Don't rely on the last four characters of an address. Compare the whole thing.
⚠️ One more note: 4.8.3 adds signature checks for unconfirmed transactions, but it doesn't turn Electrum into a full Bitcoin node.
🟢 Bullish scenario
Users update quickly, the fix closes the hole, and the incident ends with two reports and a patched wallet.
🔴 Risk scenario
Many people stay on old versions, attackers keep running malicious servers, and more fee-bump thefts follow.
👀 Three things to watch
1️⃣ Update adoption: how fast do users move to 4.8.3?
2️⃣ New incident reports: do more thefts surface beyond the two confirmed?
3️⃣ Other wallets: do similar wallets add the same checks?
💡 The key takeaway
The fix is out and the defense is simple: update and check the full address before you sign. A fee bump looks routine, which is exactly why it's dangerous.
That is the part worth watching.
This post is for informational and educational purposes only and is not financial advice. Crypto markets are volatile. Always conduct your own research before making financial decisions.
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