A channel-close vulnerability in LND, a Lightning Network node implementation, could risk an entire channel's balance in a reproduced worst-case scenario. Operators running standard releases below version 0.21.0 should consider their nodes exposed unless they have applied independent patches.
According to an Aug. 13 disclosure published by Bastien Teinturier, a malicious channel peer could combine a one-block Bitcoin reorganization with an old, revoked commitment transaction following a cooperative close. The disclosure noted that no affected users were known at the time.
Prior to the fix, LND could forget a cooperatively closed channel after the closing transaction received its first on-chain confirmation. This removal left the node without the channel state necessary to respond safely if Bitcoin subsequently reorganized that block out of the chain.
Executing the attack involves specific conditions. A malicious peer must participate in the cooperative close, wait for a single confirmation, and leverage a reorganization that removes the closing transaction. Additionally, the peer must possess and publish an earlier revoked commitment representing an outdated channel balance state that typically triggers a penalty.
Under this scenario, an affected LND node may fail to broadcast the penalty transactions meant to punish the publication of the revoked state. The resulting loss can reach the channel's full balance under maximum-loss testing conditions, though this does not indicate active exploitation in the wild. The vulnerability and its fix are specific to LND and do not imply that other Lightning implementations share the same flaw.
Repository history indicates that the official fix begins with version 0.21.0, correcting an earlier citation of version 0.20.0 in the public disclosure. Pull request #10331 was merged into the project's master branch on Jan. 16, 2026. A backport to the 0.20.x branch was subsequently reverted, and documentation updates confirmed the reorganization-safe close logic arrived in the 0.21.0 release line.
Node operators are advised against relying on the 0.20.0 cutoff mentioned in initial disclosures. Standard releases preceding 0.21.0 should be treated as lacking the official fix unless patched independently. LND's security policy encourages running the latest minor release of the newest major line supported, which included lnd v0.21.2-beta as of Aug. 25. The updated logic ensures LND retains close state while waiting for multiple confirmations and reacts to reorganization notifications instead of treating channels as resolved after a single block.
