Bitcoinjs-lib, a library used to construct Bitcoin functions, has patched two bugs that may make software program understate the miner payment a sound transaction would pay if broadcast and accepted.
The Oct. 26 safety disclosures establish fixes in variations 5.2.2, 6.1.9 and seven.0.4 for the corresponding launch traces.
The affected format is {a partially} signed Bitcoin transaction (PSBT), and BIP 174 defines it as a strategy to move transaction info and signatures between purchasers. Signing, combining signatures, finalizing inputs, and extracting the transaction are separate features, even when one software performs a number of of them.
The danger issues functions that import these packages and belief bitcoinjs-lib’s payment calculation or excessive-fee safeguard with out independently checking the outputs being spent. Maintainers must overview their dependency model and the way they validate imported PSBTs.
Why legitimate signatures can accompany deceptive charges
A Bitcoin transaction’s payment is the distinction between the worth of its inputs and its outputs, so understating an enter makes the calculated payment look smaller.
Within the first flaw, signing and payment accounting can use totally different values for a similar enter. Signing makes use of the total earlier transaction, whereas payment accounting prefers a conflicting report containing a smaller worth. Consequently, the weak software program can authorize the actual transaction whereas evaluating the mistaken payment.
The advisory describes an indication on bitcoinjs-lib 7.0.1 through which the precise payment was 900,000,000 satoshi, however the library reported 200 satoshi. The signature verified, and extraction returned with out the default fee-rate warning.
The second advisory describes finalized inputs with each input-value data lacking. The calculator counts these inputs as zero, and an already-signed PSBT imported from one other occasion can attain this calculation with no need one other signing operation.
Its hypothetical instance has a real payment of 91,000 satoshi however a reported payment of 1,000 satoshi. Finalized scripts and signatures alone don’t set up the lacking enter’s worth.
Precise loss requires a certified, legitimate transaction to be broadcast and accepted by the community. These defects don’t create signatures, and extra worth turns into a miner payment.
For conflicting data, affected releases are 5.2.0 via 5.2.1, 6.0.0 via 6.1.8 together with 6.1.0-rc.0, and seven.0.0-rc.0 via 7.0.3. The missing-record flaw impacts the identical v6 and v7 ranges, plus 5.1.0 via 5.2.1 within the v5 line.
The remediation offers signing and accounting a shared methodology for resolving earlier outputs, rejects conflicting values or scripts, and requires an quantity for each enter throughout payment calculation. It additionally clears cached charges and extracted transactions after related metadata modifications or mixtures.
Maintainers unable to improve ought to independently confirm referenced output values. Reject conflicting data earlier than signing or trusting charges, and confirm each enter worth earlier than trusting charges or extracting a transaction.
