Eclair fixes Bitcoin Lightning fees vulnerability

Overview

Eclair, ACINQ's Lightning node software, has made significant strides in improving its security and stability. The latest updates, which merged on October 2 and October 5, address two critical vulnerabilities that could have led to financial losses for users. These fixes, PR #3388 and PR #3390, aim to safeguard channel funding and splicing operations against malicious actors.

PR #3388: Peer-Initiated Replace-By-Fee Limitations

The first repair, PR #3388, focuses on peer-initiated replace-by-fee (RBF) attempts during dual-funded channel openings or splices. In such scenarios, a malicious peer could request a replacement transaction with an arbitrary fee rate, potentially leading to a loss for the contributing node. The repair rejects such attempts above the maximum funding fee rate recommended by Eclair, ensuring that the contributing node is not left vulnerable to such exploits.

PR #3390: Backend Compromise Protection

The second repair, PR #3390, addresses a separate threat in Eclair-signer mode. A compromised Bitcoin backend, such as bitcoind, could report a fee within budget while constructing a transaction that actually paid more. This could lead to missing change, which would result in the attacker spending funds without paying an attacker's address. The repair calculates the actual fee from the amounts of the coins being spent, checks that the backend's reported fee matches, and applies the budget to the actual fee. It also verifies that Eclair's rebuilt contributions pay the same verified fee and rejects invalid change-output positions.

Conclusion

These critical fixes demonstrate Eclair's commitment to improving the security and stability of its Lightning node software. Operators are advised to check that their installed build contains the October changes to ensure the continued safety of their channel funding and splicing operations.