Monero shaken by block reorg, reviving tensions with Qubic

Privacy-centric blockchain Monero suffered an 18-block reorganization that invalidated more than 100 transactions, spurring warnings for users to wait beyond the network’s typical 10 confirmations before accepting payments.

Reorganizations occur when two competing versions of a proof-of-work chain are mined, and the network later converges to the longer, higher-difficulty chain. This ultimately discards the other’s recent blocks and any transactions inside them. While rare at this length, reorgs are a known operational risk for any PoW network, and merchants typically mitigate them by waiting a set number of confirmations before treating a payment as final.

Monero Research Lab, an unofficial project focused on XMR, said nodes observed an alternate chain 18 blocks long starting at height 3,499,659, which left roughly 117–118 transactions on the orphaned branch for almost 40 minutes. Because the event exceeded nine blocks, Monero’s standard 10-block lock did not protect all affected transactions from being rolled back, the group noted.

The project advised developers to weigh temporarily rolling DNS checkpoints to harden the network’s defenses in the near term. Yu Xian, co-founder of onchain security firm SlowMist, also warned that ignoring reorg risk could enable double spends even without a clear majority of hash power.

Speculation over the reorg’s source surfaced quickly after the Sept. 14 alert. Several community accounts pointed to prior tensions with Qubic, which previously claimed outsized Monero hashrate. The unknown mining pool involved fueled assumptions around Qubic's involvement, as the protocol previously stopped reporting its hashrate in public data providers.

Monero community podcaster Xenu stated that Qubic may have mined in isolation, using a variant of “selfish mining” even after earlier reorg attempts. “This is the largest reorg in Monero's history,” the user posted on X.

In selfish mining, a miner withholds newly found blocks to build a private fork and then publishes it in one burst to overtake the public chain, exploiting proof-of-work’s preference for the chain with the most cumulative work.

Qubic founder Sergey Ivancheglo rejected some of those assertions in social media posts. He said that Xenu “pulled all that out of his ass,” referring to the podcaster’s claims of Qubic’s role in the incident.

Notably, Monero’s native token seems to have benefited from the debacle. XMR rose over 6% in the last 24 hours while QUBIC traded flat, according to The Block’s price page.

The latest event follows months of debate inside the Monero ecosystem about reorg exposure and boasts from outside actors about controlling large shares of the network’s mining power. Earlier this year, XMR community members traded barbs with Qubic proponents after Ivancheglo’s project reportedly amassed around 51% of the network’s hashrate.