The Monero (XMR) network recently experienced a rare and significant event: an 18-block blockchain reorganization. This has raised serious alarms within the crypto community, as it suggests the network may now be vulnerable to double-spending attacks.
A blockchain reorganization occurs when a new, longer version of the blockchain is created, replacing an existing chain. While minor reorgs of one or two blocks can happen naturally, an 18-block reorg is highly unusual. It effectively rewrote more than half an hour of Monero's transaction history, leading experts to believe it was caused by abnormal mining power or deliberate manipulation.
This event now puts the network at risk. According to a security researcher from SlowMist, the ability to execute a double-spend attack now exists, even without a full 51% control of the network's hash rate.
Following the reorg, the long-standing practice of waiting for 10 transaction confirmations before considering a transfer final is no longer considered safe. A malicious actor could send a payment, wait for it to be confirmed 10 times, and then have the entire transaction invalidated by a deeper chain reorganization, allowing them to effectively "double-spend" the coins.
This isn't the first time Monero has faced these concerns. Earlier this year, reports of a controversial mining project gaining a majority of the network's hash power led major exchanges like Kraken to temporarily suspend XMR deposits. The recent reorg appears to validate those earlier fears, as on-chain data shows large mining pools competing to build the longest chain, pushing out blocks from smaller miners.
Moving forward, Monero users and merchants are advised to wait for a significantly higher number of confirmations before accepting an XMR transaction as final.
September 2025, Cryptoniteuae