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

On Friday and Saturday, the Litecoin network experienced a significant disruption due to a denial-of-service attack, which allowed invalid transactions to be processed. The attack exploited a vulnerability in the Mimblewimble Extension Block (MWEB) protocol, enabling the invalid transactions to bypass nodes that had not been updated. However, the network's longest valid chain eventually corrected the transactions. The Litecoin Core v0.21.5.4 release has been made available, which includes important security updates to prevent similar attacks in the future. According to the Litecoin Foundation, the bug was fully patched, and the network is now operating normally. Nevertheless, security researchers have raised concerns regarding the timeline of the patch, suggesting that the vulnerability was known and patched privately a month prior to the attack. The consensus vulnerability was privately patched between March 19 and March 26, but the fix was not publicly disclosed or mandated for all mining pools, creating a window of vulnerability. The attackers seemed to be aware of the patched and unpatched nodes, exploiting this knowledge to carry out the attack. Blockchain data indicates that the attacker had pre-funded a wallet 38 hours before the exploit, with the intention of swapping LTC for ETH on a decentralized exchange. The denial-of-service attack and the MWEB bug were separate components, designed to take patched mining nodes offline and allow unpatched nodes to form a chain that included the invalid transactions. The network's ability to automatically handle the 13-block reorganization once the DoS stopped suggests that enough hashrate was running updated code to eventually overpower the attack. The incident highlights the differences in how various networks respond to exploits, with newer chains having more centralized validator sets and being able to coordinate upgrades quickly, whereas older proof-of-work networks like Litecoin rely on independent mining pools to choose when to upgrade, creating a window of vulnerability.