On Friday and Saturday, a series of events unfolded as a 13-block chain reorganization occurred on the Litecoin network, effectively rewinding 32 minutes of network activity. This was in response to an attack that exploited a vulnerability in the Mimblewimble Extension Block protocol. The attackers utilized a denial-of-service attack against major mining pools, allowing invalid transactions to temporarily bypass nodes that had not been updated. However, the network's longest valid chain eventually corrected these transactions.
In response to the incident, Litecoin Core v0.21.5.4 has been released, with all users advised to upgrade due to important security updates. According to the Litecoin Foundation, the bug has been fully patched and the network is operating normally.
Nevertheless, security researchers have pointed out discrepancies in the timeline of events, suggesting that the vulnerability was known and privately patched roughly four weeks before the attack. The fact that some miners were running patched code while others were still vulnerable created an opportunity for the attackers to exploit this window. Further analysis has revealed that the attacker had 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 reportedly separate components, with the DoS designed to take patched mining nodes offline. 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. This incident highlights the differences in how various networks respond to exploits, with newer chains often coordinating upgrades more quickly and older proof-of-work networks like Litecoin and bitcoin relying on independent mining pools to choose when to upgrade.