18 Block Reorg Slams Monero, Erasing 36 Minutes Of Blockchain

Monero’s privacy chain endured its deepest-ever chain reorganization in the last 24 hours, when 18 consecutive blocks were replaced, briefly “rewriting” roughly 36 minutes of ledger history and invalidating about 118 already-confirmed ￰1￱ independent monitors flagged the event late Sunday into Monday, describing a rollback spanning block heights 3,499,659 through 3,499,676 before nodes converged on a new best ￰2￱ Monero targeting two-minute blocks, an 18-block reorg translates to ~36 minutes of history—an extraordinary depth for a mature proof-of-work ￰3￱ Hit By Record 18 Block Reorg “The attack against Monero is ￰4￱ ago XMR experienced an 18-block ￰5￱ you accept XMR make sure to wait for more than the usual 10 confs,” warned independent monitor OrangeFren as alerts circulated across crypto social ￰6￱ post, amplified by several industry accounts, captured the immediate operational takeaway for merchants and services: raise confirmation thresholds until conditions ￰7￱ incident comes a month after the controversial AI-oriented projec t Qubic claimed to have marshaled a majority of Monero’s hashrate, a campaign that coincided with a six-block reorg in August and led to temporary deposit suspensions at some ￰8￱ researchers at the time cautioned that the August event did not, by itself, prove sustained 51% dominance—streaks of mining “luck” can produce short, probabilistic reorganizations—but they also warned that persistent hashrate concentration raises the ceiling on how deep such reorgs can go.

Monday’s 18-block episode materially raises that ￰9￱ voices reacted with a mix of alarm and ￰10￱ founder Yu Xian commented via X: “If no one in the Monero community takes the issue of block reorganization seriously, then this Sword of Damocles will always hang over Monero’s head… It may not necessarily carry out a double-spend attack, but having this capability… It doesn’t even have to strictly exceed 51% of the hash power…” Qubic founder Sergey Ivancheglo, who is known by the alias “Come-from-Beyond”, posted via X: “Monero will stay because Qubic wanted it to stay.” #Monero will stay because #Qubic wanted it to stay. ￰0￱ ￰11￱ — Come-from-Beyond (@c___f___b) September 14, 2025 At a technical level, a chain reorg occurs when two valid histories compete and the network ultimately converges on the one with the most accumulated proof-of-work, discarding the other and any transactions exclusive to ￰12￱ Monero’s design, two-minute target block intervals and dynamic block sizing aim to keep throughput smooth while preserving privacy primitives like ring signatures and stealth ￰13￱ practice, however, a miner or pool with outsized hashpower can—at least in bursts—privately extend a side chain and then release it, “out-working” the public tip and forcing nodes to ￰14￱ is what appears to have happened here, with a depth that exceeded the de facto 10-confirmation comfort zone commonly used by wallets and ￰15￱ August–September sequence has re-opened a contentious debate inside Monero about ￰16￱ span the spectrum: “rolling 10-block checkpoints” that finalize recent blocks to cap reorg depth; adopting elements akin to Dash’s ChainLocks to bolt on a finality layer; “detective mining” incentives to counter selfish-mining strategies at the pool level; and even merge-mining concepts that would piggyback Monero’s security on a larger PoW ￰17￱ trade-off is sharp: checkpoints and ChainLocks introduce degrees of centralization or new trust assumptions, while pool-level changes may be unevenly ￰18￱ community has not yet coalesced around a specific fix, but the urgency has unmistakably ￰19￱ treated the event with surprising ￰20￱ hours, XMR rallied between roughly 5% and 7%, trading above $300 on some venues.