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 reorganization was in response to an attack that exploited a vulnerability in the Mimblewimble Extension Block (MWEB) protocol, allowing for invalid transactions to bypass nodes that had not been updated. The Litecoin Core v0.21.5.4 release has since 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 a month prior to the attack, but the fix had not been publicly disclosed or mandated for all mining pools. This created a window of opportunity for attackers, who seemed to be aware of which miners were running the patched code and which were still vulnerable. The attackers pre-funded a wallet 38 hours before the exploit and had configured the destination address to swap LTC for ETH on a decentralized exchange. The denial-of-service attack and the MWEB bug were separate components, with the DoS designed to take patched mining nodes offline so that the unpatched ones would form the chain that included the invalid transactions. The automatic handling of the 13-block reorganization by the network once the DoS stopped suggests that enough hashrate was running updated code to eventually overpower the attack. This incident highlights the differences in how code maintainers and developers react to exploits across various networks, with newer chains being able to coordinate upgrades quickly and older proof-of-work networks like Litecoin and Bitcoin relying on independent mining pools to choose when to upgrade, creating a window of vulnerability.