On Friday and Saturday, a series of events unfolded as a 13-block chain reorganization on the Litecoin network occurred, effectively rewinding 32 minutes of network activity. This reorganization was in response to a denial-of-service attack that exploited a vulnerability in the Mimblewimble Extension Block (MWEB) protocol, allowing invalid transactions to 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 consensus vulnerability was known and privately patched between March 19 and 26, roughly four weeks before the attack. 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 attack involved a denial-of-service component designed to take patched mining nodes offline, allowing unpatched nodes to form a chain that included invalid transactions. 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 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 various networks respond to exploits, with newer chains often coordinating upgrades more swiftly than older proof-of-work networks like Litecoin and Bitcoin.