A single locked output can be spent several times inside one transaction, minting value from nothing
- Severity
- Critical
- Class
- Value integrity
- System
- Privacy chain (multi-signature consensus)
A party who can sign for one locked amount can list it many times in a single valid transaction, creating funds that never existed and draining escrow.
Consensus assumed each input in a transaction was distinct, and checked each one on its own without asking whether the same one appeared twice. Someone able to sign for a single locked output could reference it repeatedly in one transaction, and every reference was counted as real.
That turns one unit of value into many. The transaction passes full validation, so the minted amount is indistinguishable from legitimately created funds.
Why it rated Critical
Coin inflation and theft of escrowed funds strike at the core invariant of any ledger — that value can't be created by spending. It required only the ability to sign for one output an attacker already controlled.
The fix class
Enforce intra-transaction uniqueness on inputs, so the same output can never be counted more than once in a single transaction.
