Late Friday and Saturday, a series of events unfolded on the Litecoin network, involving a denial-of-service attack and a 13-block chain reorganization. The attack, which occurred at a price of $55.44, rewound approximately 32 minutes of network activity. This was made possible by a vulnerability in the Mimblewimble Extension Block (MWEB) protocol, which allowed invalid transactions to bypass nodes that had not been updated. The Litecoin Core v0.21.5.4 release, which includes important security updates, has been made available, and all users are advised to upgrade.

According to the Litecoin Foundation, the bug was fully patched, and the network is operating normally. However, security researchers have pointed out discrepancies in the timeline of events, suggesting that the vulnerability was privately patched between March 19 and 26, roughly four weeks before the attack.

The consensus vulnerability that allowed the invalid MWEB peg-out was known and patched privately a month before the exploit, but the fix had not been broadcast publicly or required for all mining pools. This created a window of opportunity for the attackers, who appeared to be aware of which miners were running the patched code and which were still vulnerable.

The attackers 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 automatic handling of 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 being able to coordinate upgrades quickly and older proof-of-work networks like Litecoin and bitcoin relying on independent mining pools to choose when to upgrade, creating a window of vulnerability.