A recent update to Bitcoin Core addresses a flaw in the way partially signed Bitcoin transactions can be constructed, a development that may affect how wallets and hardware signing devices handle user-authorized payments. The change, merged into Bitcoin Core’s master development branch on September 25, responds to a narrow issue involving SIGHASH_SINGLE, a signing mode that previously allowed a signature to be created without fully binding funds to the intended recipient address. While the vulnerability does not expose private keys, it permits a signature to remain valid even when the transaction’s destination is altered under specific conditions. The risk primarily affects legacy Bitcoin inputs; SegWit v0 transactions retain stronger safeguards because they continue to commit to the specific coin being spent. Bitcoin Core’s new code integrates the check into shared signature-creation logic, blocking the problematic configuration from reaching the signing stage while preserving functionality for valid inputs. This reinforces the principle that a cryptographic signature must reflect the exact transaction details a user has approved. The fix aligns with guidance in Bitcoin Improvement Proposal 174, which advises signers to reject insecure signing modes and favor SIGHASH_ALL when no alternative is specified. Wallet providers and hardware signing integrations are now tasked with independently verifying their handling of SIGHASH_SINGLE requests, as the updated Bitcoin Core code does not yet appear in a publicly released version. The change underscores ongoing efforts to strengthen transaction integrity without compromising the decentralized architecture of the Bitcoin network.