Firo Hard Fork Targets Spark Vulnerability Ahead of Block 1,371,000

Firo’s blockchain is set to undergo a hard fork at block 1,371,000, estimated to occur around 10 a.m. UTC on September 4. The upgrade is mandatory for anyone running Firo software, including wallet users, full‑node operators, masternodes, miners and exchanges.

Why the Upgrade Is Critical

The fork addresses a vulnerability disclosed on August 13 in Spark, Firo’s privacy‑preserving transaction protocol. The flaw affects multi‑input Spark spends and, under specific conditions, could allow the creation of forged FIRO tokens, inflating the supply.

Interim Mitigation

Version 0.14.17.2 temporarily limited Spark transactions to a single input, reducing privacy but preserving supply integrity. This stopgap required users to split larger private payments into multiple single‑input transactions.

Permanent Fix in v0.14.18.0

The upcoming v0.14.18.0 release introduces a new Chaum V2 proof and transaction format, restoring normal multi‑input Spark spending while continuing to validate historic transactions. Existing balances, addresses and wallet keys remain valid; no fund migration is needed.

Deadline and Compatibility

Nodes that do not upgrade before the fork will become incompatible with the upgraded network after block 1,371,000. The block height, not the clock, determines when the new rules take effect.

Next Steps

Firo plans to publish a detailed technical disclosure and post‑mortem after the fork activates.