bitcoinjs-lib: Undetected merkle node duplication in block root computation validates a forged transaction list

Overview

bitcoinjs-lib is a JavaScript Bitcoin library for Node.js and browsers. From 2.3.0 until 5.2.1, 6.1.8, and 7.0.2, fastMerkleRoot pads odd Merkle-tree levels by hashing the final node with itself but does not report adjacent duplicate hashes. The affected block-root verifier was introduced as Block.checkMerkleRoot() alongside Block.calculateMerkleRoot(), while later versions expose validation through checkTxRoots() and __checkMerkleRoot; these validation paths can accept a recomputed root without checking for mutation. A peer can append duplicate transactions so a different transaction list retains the original Merkle root, block header, proof of work, and block identifier. Consumers that rely on block-root validation, including explorers, exchange indexers, or SPV clients, can process a duplicated transaction twice or blacklist the shared block hash and reject the honest block. This issue is fixed in versions 5.2.1, 6.1.8, and 7.0.2.

Affected

• bitcoinjs-lib >= 2.3.0, < 5.2.1
• bitcoinjs-lib >= 6.0.0, < 6.1.8
• bitcoinjs-lib >= 7.0.0-rc.0, < 7.0.2

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.