Litecoin Recovers from Denial-of-Service Attack by Rewriting 13 Blocks

Late Friday and Saturday, a series of events unfolded as a 13-block chain reorganization on the Litecoin network rewound approximately 32 minutes of network activity. This action was taken in response to a denial-of-service attack that exploited a vulnerability in the Mimblewimble Extension Block (MWEB) protocol, allowing invalid transactions to temporarily bypass nodes that had not been updated. The Litecoin Core v0.21.5.4 release has been made available, advising all users to upgrade due to important security updates. According to the Litecoin Foundation, the bug has been fully patched, and the network is now operating normally. However, security researchers have pointed out discrepancies in the timeline of events, suggesting that the vulnerability was known and patched privately between March 19 and 26, roughly four weeks before the attack occurred. The consensus vulnerability that allowed the invalid MWEB peg-out was privately addressed during this period, but the fix was not publicly disclosed or mandated for all mining pools. This created a window of opportunity for attackers, who seemed to be aware of which nodes were patched and which were still vulnerable. The attack involved a denial-of-service component designed to take patched mining nodes offline, allowing unpatched nodes to form a chain that included the invalid transactions. Blockchain data reveals that the attacker pre-funded a wallet 38 hours before the exploit, using a Binance withdrawal, and had configured the destination address to swap LTC for ETH on a decentralized exchange. The automatic handling of the 13-block reorganization by the network once the denial-of-service attack stopped suggests that enough hashrate was running updated code to eventually overpower the attack. This incident highlights the differences in how various networks respond to exploits, with newer chains capable of coordinating upgrades quickly and older proof-of-work networks like Litecoin and Bitcoin facing challenges due to their reliance on independent mining pools choosing when to upgrade.