Impact

The btcd Bitcoin client (versions 0.10 to 0.24) did not correctly re-implement Bitcoin Core's "FindAndDelete()" functionality. This logic is consensus-critical: the difference in behavior with the other Bitcoin clients can lead to btcd clients accepting an invalid Bitcoin block (or rejecting a valid one).

This consensus failure can be leveraged to cause a chain split (accepting an invalid Bitcoin block) or be exploited to DoS the btcd nodes (rejecting a valid Bitcoin block). An attacker can create a standard transaction where FindAndDelete doesn't return a match but removeOpCodeByData does making btcd get a different sighash, leading to a chain split. Importantly, this vulnerability can be exploited remotely by any Bitcoin user and does not require any hash power. This is because the difference in behavior can be triggered by a "standard" Bitcoin transaction, that is a transaction which gets relayed through the P2P network before it gets included in a Bitcoin block.

FindAndDelete vs. removeOpcodeByData

removeOpcodeByData(script []byte, dataToRemove []byte) removes any data pushes from script that contain dataToRemove. However, FindAndDelete only removes exact matches. So for example, with script = "<data> <data||foo>" and dataToRemove = "data" btcd will remove both data pushes but Bitcoin Core's FindAndDelete only removes the first <data> push.

Patches

This has been patched in btcd version v0.24.2-beta.

References

FindAndDelete: https://github.com/btcsuite/btcd/security/advisories/GHSA-27vh-h6mc-q6g8

btcd before 0.24.0 does not correctly implement the consensus rules outlined in BIP 68 and BIP 112, making it susceptible to consensus failures. Specifically, it uses the transaction version as a signed integer when it is supposed to be treated as unsigned. There can be a chain split and loss of funds.

Lightning Network Daemon (lnd) is an implementation of a lightning bitcoin overlay network node. All lnd nodes before version v0.15.4 are vulnerable to a block parsing bug that can cause a node to enter a degraded state once encountered. In this degraded state, nodes can continue to make payments and forward HTLCs, and close out channels. Opening channels is prohibited, and also on chain transaction events will be undetected. This can cause loss of funds if a CSV expiry is researched during a breach attempt or a CLTV delta expires forgetting the funds in the HTLC. A patch is available in lnd version 0.15.4. Users are advised to upgrade. Users unable to upgrade may use the lncli updatechanpolicy RPC call to increase their CLTV value to a very high amount or increase their fee policies. This will prevent nodes from routing through your node, meaning that no pending HTLCs can be present.

btcd before 0.23.2, as used in Lightning Labs lnd before 0.15.2-beta and other Bitcoin-related products, mishandles witness size checking.

Bitcoin Core 0.16.x before 0.16.2 and Bitcoin Knots 0.16.x before 0.16.2 allow remote denial of service via a flood of multiple transaction inv messages with random hashes, aka INVDoS. NOTE: this can also affect other cryptocurrencies, e.g., if they were forked from Bitcoin Core after 2017-11-15.