lnd 0.21.5 force-closes taproot overlay channels with missing aux signatures

Serguey Asael Shinder28 October 2026, 09:192 min read

Lightning Labs published lnd v0.21.5-beta on 27 October, together with a 0.20.6-beta maintenance release. The 0.21.5 notes list no database migrations; the changes are bug fixes, several of which alter behaviour.

The one most likely to be noticed: validation of auxiliary HTLC signatures on taproot overlay channels is tightened, so their count must match the number of HTLCs on the commitment, as already required for the BTC-level signatures. A commitment that fails is rejected as invalid, which force-closes the channel. The notes name the affected setup — a taproot overlay channel whose peer runs lnd without an aux signer attached, for example with tapd stopped. Such peers' commitments used to be accepted, leaving HTLCs with empty auxiliary signatures that could not be swept at force close. Peers running an older tapd with the signer attached are unaffected.

Other fixes: a deadlock in the native SQL connection pool, where two SubscribeInvoices calls with a non-zero settle_index on SQLite could take every pool connection and block all database access; fee estimates from an external fee.url API are now capped at 10,000 sat/vB, where previously only a floor was applied; and lnd no longer proposes a commitment fee rate below 253 sat/kw, which could happen with max-commit-fee-rate-anchors=1 or a backend reporting fees below the minimum. lnd now tries to raise such channels to the minimum and warns at startup about the setting. Revocation processing reorders its checks ahead of bookkeeping, and TLV decoding no longer reserves the full encoded length up front.

What it means

Most of this is defensive: limits on values that arrive from outside — a peer's signatures, an external fee API, a declared TLV length. The taproot overlay change is the operational one. Operators of taproot asset channels should check that every peer runs with its aux signer attached before upgrading, because the new rule converts a latent sweep problem into an immediate force close.