Eclair merges fixes for Lightning flaws that could burn Bitcoin in fees

Eclair, ACINQ’s Lightning node software program, has merged two repairs for gaps that could make a node lose Bitcoin via extreme mining fees throughout channel funding and splicing. One limits a peer’s fee-bump calls for when Eclair contributes funds; the opposite checks transactions from a compromised Bitcoin backend whereas Eclair retains the signing keys.

The repairs merged into the challenge’s grasp department on Oct. 2 and Oct. 5. As of Oct. 12, its release page nonetheless listed September’s v0.14.3 as newest. The two October fixes postdate that packaged launch.

Bitcoin Optech’s Oct. 9 newsletter highlighted each adjustments as closing safety gaps throughout twin funding and splicing.

The first restore, PR #3388, considerations peer-initiated replace-by-fee, or RBF, makes an attempt throughout a dual-funded channel opening or a splice that adjusts a channel’s funding. A peer could request a alternative transaction with the next charge fee. Eclair saved its pockets contribution and paid for its inputs at that fee, with out an higher certain or charge funds on this path.

That let a malicious peer impose an arbitrary mining charge fee on the contributing node whereas contributing nothing itself. The loss can be paid as fees to miners quite than transferred on to the peer.

The restore rejects makes an attempt above the utmost funding charge fee Eclair recommends to its peer. Two exceptions stay: the peer buys liquidity and pays the fees for Eclair’s inputs, or the Eclair node contributes no funds to the transaction. In these circumstances, Eclair doesn’t bear the fee addressed by this restrict.

Keeping keys is simply a part of the protection

PR #3390 addresses a separate menace in Eclair-signer mode. Bitcoin Core’s backend, bitcoind, selects cash and builds transactions, whereas Eclair retains the keys and indicators.

A compromised backend could report a charge inside funds whereas developing a transaction that truly paid extra, together with by dropping the change output. Under Bitcoin’s transaction accounting, enter worth not assigned to outputs turns into a miner charge. Missing change can subsequently spend funds with out paying an attacker’s deal with.

When a charge funds is equipped, the restore calculates the precise charge from the quantities of the cash being spent, fetched by transaction ID to authenticate their values. It checks that the backend’s reported charge matches and applies the funds to the precise charge. It additionally checks that Eclair’s rebuilt contributions pay the identical verified charge and rejects invalid change-output positions.

These are distinct from the cooperative-closing fee flaw lined in CryptoSlate’s September report and the restart denial-of-service issues lined Oct. 2.

These repairs deal with Eclair’s dual-funding, splicing and signer configurations. Operators ought to examine that their put in construct accommodates the October adjustments.

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