On Friday and Saturday, a chain reorganization of 13 blocks occurred on the Litecoin network, effectively undoing 32 minutes of network activity after attackers leveraged a vulnerability in the Mimblewimble Extension Block protocol to initiate a denial-of-service attack against major mining pools. The attack allowed invalid transactions to bypass nodes that had not been updated, before the network's longest valid chain rectified the issue. Following the incident, Litecoin Core v0.21.5.4 was released, with users advised to upgrade due to important security updates. According to the Litecoin Foundation, the bug was fully patched and the network resumed normal operation by Sunday morning.
However, security researchers have pointed out discrepancies in the timeline of events, citing the litecoin-project GitHub repository, which indicates the consensus vulnerability was privately patched a month prior to the attack. The vulnerability allowed for a window of exploitation, as some miners were running patched code while others were still using the vulnerable version. The attackers seemingly took advantage of this knowledge to execute the denial-of-service attack and include invalid transactions in the chain.
Blockchain data reveals the attacker had pre-funded a wallet 38 hours before the exploit, with plans to swap the stolen 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 ones to form a chain that included the invalid transactions. The network's automatic handling of the 13-block reorganization once the DoS stopped suggests sufficient 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 quickly and older proof-of-work networks like Litecoin relying on independent mining pools to choose when to upgrade, creating potential windows of vulnerability.