Bitcoin developer Antoine Riard, a well-known member of the Lightning Network community, announced his departure from the project after disclosing a major vulnerability.
In an announcement on Oct. 20, the developer said he was halting his involvement with Lightning and its implementations effective immediately.
“I think this new class of replacement cycling attacks puts lightning in a very perilous position, where only a sustainable fix can happen at the base-layer, e.g adding a memory-intensive history of all-seen transactions or some consensus upgrade,” said Riard in his note.
The Lightning Network is a Layer 2 solution for the Bitcoin blockchain that aims to address some of the issues associated with Bitcoin’s scalability and high transaction fees. It enables faster, cheaper, and more private transactions, making it a crucial part of the Bitcoin ecosystem.
The vulnerability Riard highlighted would allow malicious actors to steal funds from the Lightning Network by executing what he describes as “a transaction relay jamming attack.”
The attackers could target Lightning’s Hash Time Locked Contracts (HTLC), disrupting the normal flow of transactions and preventing them from being processed, potentially leading to a loss of funds on its channels.
4/ By securing the HTLC on each hop with the same hashlock, payments can be routed atomically.
Carol can't claim the outgoing HTLC without revealing the preimage, which Bob can then use to redeem the incoming HTLC from Alice.
At least that's the theory…
— mononaut (@mononautical) October 21, 2023
After some misrepresentations of Riard’s post began to appear on Twitter, he clarified in another post that the security flaws he raised were not, in fact, “intentional backdoors” that would question the competence and know-how of the Bitcoin and Lightning development community.
“In the meanwhile, lightning experts have already deployed mitigations which are hardening the lightning ecosystem significantly in face of simple or medium attacks,” said Riard.
He noted that more sophisticated attacks could only be executed if developers had sufficient peer-to-peer and mempool knowledge and months of preparation.