Researchers disclose routed Lightning payment atomicity weakness
Developers disclosed a Lightning Network weakness in which on-chain fee pressure could undermine the atomic safety of routed HTLC payments.
Matt Corallo disclosed an attack affecting routed Lightning payments that relied on the interaction between HTLC timeouts and Bitcoin's fee market. In a routed payment, different channel hops use time-locked contracts so that either everyone gets paid or the payment unwinds.
The weakness arose if an adversary could keep a necessary on-chain settlement transaction from confirming before its timeout, especially during sustained high fee pressure. That could allow one party in a route to claim funds while another failed to recover them.
The issue was not evidence of active theft in April 2020. It was a protocol-safety disclosure that exposed how second-layer security depends on reliable access to Bitcoin block space during disputes, and it contributed to later work on anchor outputs and fee-bumping mechanisms.