GHSA-hfcf-v2f8-x9pc bitcoinj has a ScriptExecution P2PKH/P2WPKH Verification Bypass

• Maven org.bitcoinj:bitcoinj-core: >= 0.15, < 0.17.1 → fixed in 0.17.1

Summary `ScriptExecution.correctlySpends()` contains two fast-path verification bugs for standard `P2PKH` and native `P2WPKH` spends in `core/src/main/java/org/bitcoinj/script/ScriptExecution.java`. In both branches, bitcoinj verifies an attacker-controlled signature/public-key pair but fails to verify that the public key is the one committed to by the output being spent. As a result, any attacker keypair can satisfy bitcoinj's local verification for arbitrary `P2PKH` and `P2WPKH` outputs. This doesn't affect the SPV (simple payment verification) trust model, as this model follows PoW and doesn't verify input signatures at all. Details The issue is in the optimized branches of `ScriptExecution.correctlySpends(...)`. In the `P2PKH` fast path at `core/src/main/java/org/bitcoinj/script/ScriptExecution.java:1042`, the code: • parses the attacker-supplied signature from `scriptSig` • parses the attacker-supplied public key from `scriptSig` • computes the sighash against the victim output's `scriptPubKey` • checks only `pubkey.verify(sigHash, signature)` It never enforces the missing `P2PKH` binding: • `HASH160(pubkey) == ScriptPattern.extractHashFromP2PKH(scriptPubKey)` That means the `OP_DUP OP_HASH160 OP_EQUALVERIFY OP_CHECKSIG` semantics are not actually enforced in this fast path. Relevant code: ```java } else if (ScriptPattern.isP2PKH(scriptPubKey)) { if (chunks.size() != 2) throw new ScriptException(...); TransactionSignature signature; try { byte[] data = Objects.requireNonNull(chunks.get(0).data); signature = TransactionSignature.decodeFromBitcoin(data, true, true); } catch (SignatureDecodeException x) { throw new ScriptException(...); } ECKey pubkey = ECKey.fromPublicOnly(Objects.requireNonNull(chunks.get(1).data)); Sha256Hash sigHash = txContainingThis.hashForSignature(scriptSigIndex, scriptPubKey, signature.sigHashMode(), false); boolean validSig = pubkey.verify(sigHash, signature); if (!validSig) throw new ScriptException(...); } ``` In the native `P2WPKH` fast path at `core/src/main/java/org/bitcoinj/script/ScriptExecution.java:1023`, the bug is similar. The code: • reads the attacker-supplied pubkey from `witness` • builds `scriptCode` from that attacker pubkey with `ScriptBuilder.createP2PKHOutputScript(pubkey)` • computes the BIP143 sighash using that attacker-derived `scriptCode` • verifies the signature against the attacker pubkey It never enforces: • `HASH160(pubkey) == ScriptPattern.extractHashFromP2WH(scriptPubKey)` So for `P2WPKH`, the attacker controls both the pubkey and the `scriptCode` used for signing. Relevant code: ```java if (ScriptPattern.isP2WPKH(scriptPubKey)) { Objects.requireNonNull(witness); if (witness.getPushCount() < 2) throw new ScriptException(...); TransactionSignature signature; try { signature = TransactionSignature.decodeFromBitcoin(witness.getPush(0), true, true); } catch (SignatureDecodeException x) { throw new ScriptException(...); } ECKey pubkey = ECKey.fromPublicOnly(witness.getPush(1)); Script scriptCode = ScriptBuilder.createP2PKHOutputScript(pubkey); Sha256Hash sigHash = txContainingThis.hashForWitnessSignature(scriptSigIndex, scriptCode, value, signature.sigHashMode(), false); boolean validSig = pubkey.verify(sigHash, signature); if (!validSig) throw new ScriptException(...); } ``` Affected call sites include: • `core/src/main/java/org/bitcoinj/core/TransactionInput.java:546` • `core/src/main/java/org/bitcoinj/wallet/Wallet.java:4520` • `core/src/main/java/org/bitcoinj/signers/LocalTransactionSigner.java:84` • `core/src/main/java/org/bitcoinj/signers/CustomTransactionSigner.java:77` These call sites use `correctlySpends()` for transaction/input validation and pre-signing checks. Any application that treats a successful result from this path as proof that a spend is valid is affected. Fix The issue is fixed on the `release-0.17` branch via 2bc5653c41d260d840692bc554690d4d79208f9c, and on `master` via b575a682acf614b9ff95cacbdeb48f86c3ababe0. A 0.17.1 maintenance release has been made available on Maven Central.