On Friday and Saturday, a series of events unfolded as a 13-block chain reorganization was executed on the Litecoin network to reverse the effects of a denial-of-service attack. The attack, which occurred at a price of $55.21, rewound approximately 32 minutes of network activity. It was made possible by a vulnerability in the Mimblewimble Extension Block (MWEB) protocol, allowing invalid transactions to bypass nodes that had not been updated.
A patch for the bug was privately implemented between March 19 and 26, more than four weeks prior to the attack. However, the fix was not publicly disclosed or mandated for all mining pools, creating a window of vulnerability. The Litecoin Core v0.21.5.4 release, which includes important security updates, has been made available, and users are advised to upgrade. According to the Litecoin Foundation, the bug has been fully patched, and the network is operating normally.
Nevertheless, security researchers have raised concerns regarding the timeline of events, pointing out that the vulnerability was known and patched a month before the exploit. The fact that some miners were running the patched code while others were still using the vulnerable version allowed the attackers to target the unpatched nodes. Blockchain data reveals that the attacker had pre-funded a wallet 38 hours before the exploit and had set up a 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, allowing the unpatched ones 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 that can coordinate upgrades quickly, whereas older proof-of-work networks like Litecoin rely on independent mining pools choosing when to upgrade, creating a window of vulnerability.