1 OP_RETURN Bug (Historical) — Glossary

TERM_DEF // SCRIPT_AUTHORIZATION / 1_OP_RETURN_BUG_HISTORICAL

1 OP_RETURN
BUG (HISTORICAL)

1 OP_RETURN Bug (Historical). Early bug allowing scripts to push 1 then OP_RETURN to short-circuit failure; long since fixed.

This page sits in the Script & Authorization section — The stack VM that decides whether a UTXO is spendable — opcodes, templates, and modern script trees. Read on for what it is, why it exists, how it works under the hood, and what to watch out for.

WHAT_1_OP_RETURN_BUG_HISTORICAL_IS

1 OP_RETURN Bug (Historical) — at a glance

SCRIPT

OP_RETURN is a Bitcoin Script opcode in the FLOW family. Its stack effect is → FAIL. Fail the script immediately; in outputs, creates a provably unspendable data carrier. Early bug allowing scripts to push 1 then OP_RETURN to short-circuit failure; long since fixed.

Why it exists

DESIGN

OP_RETURN exists because Branching gives scripts conditional spending paths — multi-sig fallbacks, Lightning HTLC timeout branches, hash-time-locked contracts.

HOW_IT_WORKS

Mechanism

HOW IT WORKS

Every UTXO is locked by a scriptPubKey — the output's locking script. To spend it, you provide a scriptSig (or witness) containing data that satisfies the lock. The node concatenates them, runs the combined script on a stack machine, and accepts the spend if and only if execution finishes with a single truthy value on the stack. 1 OP_RETURN Bug (Historical) contributes a specific stack effect within that process — opcodes either push, pop, copy, hash, branch, or verify, and they do so left-to-right deterministically.

1. The script is parsed into a sequence of opcodes and push-data items. 2. Execution starts with an empty stack and an empty alt-stack. 3. Each opcode runs in order — push opcodes add to the stack, others consume the top items and may push results. 4. Conditional opcodes (OP_IF/OP_NOTIF/OP_ELSE/OP_ENDIF) branch execution. 5. Final state: a single non-zero (truthy) value on top → the spend is authorised. Anything else (empty stack, false, error) → the script fails and the tx is rejected.

WORKED_EXAMPLE

OP_RETURN — stack effect + canonical use

EXAMPLE

Opcode : OP_RETURN Family : FLOW Stack effect: → FAIL Behaviour : Fail the script immediately; in outputs, creates a provably unspendable data carrier. Open /playground in another tab and search for OP_RETURN. Drag the opcode in, watch the stack visualisation step through it against any combination of inputs you choose.

KEY_PROPERTIES

FAMILY

Belongs to the FLOW family of Script opcodes — siblings share validation rules and historical evolution.

STACK EFFECT

Exactly → FAIL. Every full node enforces the same effect, byte-for-byte.

ACTIVE

Active on mainnet today; every spend that uses it is being validated by every full node.

CONSENSUS-CRITICAL

OP_RETURN's behaviour is consensus rule — a node implementing it differently would fork off the network.

COMMON_PITFALLS

Things that catch people out

PITFALLS

OP_RETURN is FATAL — any script execution that reaches it fails. In outputs it produces a provably unspendable "data carrier".

RELATED_CONCEPTS

Other terms from Script & Authorization — click any to read its page:

TERMINOLOGY_INDEX

TERMINOLOGY

1 OP_RETURN Bug (Historical)

Early bug allowing scripts to push 1 then OP_RETURN to short-circuit failure; long since fixed.

Script

Bitcoin's purpose-built stack language; every locking and unlocking script is a script program.

Stack

The single LIFO data structure all script execution operates on; no variables, no registers.

Locking Script

The scriptPubKey on an output; specifies the spending conditions.

Unlocking Script

The scriptSig/witness in an input; provides the data that satisfies the lock.

Redeem Script

In P2SH, the script whose HASH160 appears in the output; revealed at spend time and then executed.

Witness Script

In P2WSH, the script whose SHA256 is committed in the output; placed at the end of the witness stack.

Script Execution

Sequential stepping through opcodes, mutating the stack until either a valid truthy stack remains or the script fails.