This attack, called replacement cycling, poses a risk to the security of funds in lightning routing hops carrying HTLC traffic. Mitigations have been implemented by major lightning implementations such as LDK v0.0.118, Eclair v0.9.0, LND v0.17.0-beta, and Core-Lightning v23.08.01. The attack involves a malicious counterparty broadcasting their HTLC-preimage transaction with a higher fee and feerate than the honest HTLC-timeout of the victim lightning node. Several measures have been taken to mitigate this attack, including aggressive rebroadcasting, local-mempool preimage monitoring, and adjusting the default CLTV delta. Other bitcoin applications using bitcoin script timelocks or multi-party transactions may also be affected by denial-of-service vectors under certain levels of network mempool congestion. Developers and operators of these applications should investigate how replacement cycling attacks might disrupt their in-mempool chain of transactions or fee-bumping flows. Replacement cycling attacks pose a new way to neutralize the design goals of package relay and its companion nversion=3 policy. Full disclosure of CVEs assigned by MITRE and replacement cycling attacks took place on October 16, 2023. Despite the mitigations in place for lightning channels, developers and operators of bitcoin applications should remain vigilant and take necessary precautions to protect against replacement cycling attacks.