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A malicious bitcoin wallet server could softly swap a morganatic outgo for a thief’s transaction, past hold for its proprietor to o.k. the theft. Electrum’s latest information spot closes that loophole aft attackers exploited the flaw and stole funds.
Key Takeaways
- Electrum 4.8.3 fixes a high-severity flaw that allowed malicious servers to substitute Bitcoin transactions.
- Electrum confirmed reports of a idiosyncratic who mislaid funds aft expanding a transaction fee.
- Electrum users should upgrade instantly and verify destination addresses earlier signing transactions.
Malicious Servers Turn Bitcoin Fee Bumps Into Theft
Electrum released mentation 4.8.3 connected Saturday, informing users to upgrade instantly aft developers discovered that malicious servers were exploiting a high-severity vulnerability affecting each earlier version. The flaw, documented successful GitHub advisory GHSA-6jp4-8v48-cc5v, exploited however the lightweight Bitcoin wallet handles unconfirmed transactions.
Electrum relies connected outer servers for transaction histories, interest estimates, and broadcasting payments. While it independently checks confirmed transactions, older versions accepted definite unconfirmed transactions without verifying their signatures. Attackers turned that favoritism into a trap.
A compromised server could intercept a morganatic payment, forestall its broadcast and substitute a fraudulent transaction directing funds to an attacker-controlled bitcoin address. The replacement carried invalid signatures, yet Electrum displayed it arsenic an mean pending payment.
Four Matching Characters Help Conceal the Attack
The instrumentality became unsafe erstwhile users attempted to summation transaction fees done Replace-By-Fee (RBF). Rather than expanding the interest connected their archetypal payment, victims could inadvertently motion the substituted transaction, authorizing the transportation of their ain bitcoin to the attacker.
The deception went further. Attackers generated receiving addresses whose last 4 characters matched the intended destination, making a speedy code examination little apt to exposure the switch. One fraudulent transaction adjacent carried a zero fee, seemingly encouraging its unfortunate to initiate the precise interest accommodation needed to implicit the theft.
Developers received 2 backstage reports. On Oct. 11, idiosyncratic dannydeezy reported transaction substitution, though the fee-bump mechanics wasn’t afloat understood. On Oct. 18, Raju-K12 reported losing funds aft approving a interest increase. The 2nd study established that the onslaught wasn’t simply theoretical.
Electrum 4.8.3 Blocks the Transaction Substitution
The patch, introduced done perpetrate 90fe308, requires Electrum to verify signatures for unconfirmed transactions spending coins belonging to the wallet. Fraudulent transactions with invalid signatures are rejected earlier entering the wallet’s section history. Users moving versions earlier than 4.8.3 should download the update exclusively from electrum.org and verify its cryptographic signatures.
Until upgrading, users should cautiously inspect each destination code and outgo magnitude earlier signing, including during interest adjustments. Those connecting exclusively to trusted, self-hosted Electrum servers aren’t exposed to this peculiar server-based attack.
The incidental exposes a funny contradiction: A wallet designed to support private keys could inactive beryllium manipulated into requesting a perfectly valid signature for a outgo its proprietor ne'er intended to make.
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