An attacker exploited a vulnerability in Litecoin's Mimblewimble Extension Block (MWEB) protocol, resulting in a 13-block chain reorganization that rewound approximately 32 minutes of network activity. The bug, which was privately patched between March 19 and 26, allowed for a denial-of-service attack against major mining pools, enabling invalid MWEB transactions to bypass nodes that had not updated, before the network's longest valid chain corrected them. Following the attack, Litecoin Core v0.21.5.4 was released, containing crucial security updates.
The Litecoin Foundation reported that the bug was fully patched and the network is operating normally. However, prominent researchers have raised concerns regarding the timeline of the patch, citing the public commit log on the litecoin-project GitHub repository. The log indicates that the consensus vulnerability was known and patched privately a month prior to the exploit, but the fix had not been publicly broadcast or mandated for all mining pools, creating a window of vulnerability.
Blockchain data revealed that the attacker had pre-funded a wallet 38 hours before the exploit, with the destination address configured 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 the chain that included the invalid transactions. The network's automatic handling of the 13-block reorganization once the DoS stopped suggests that sufficient hashrate was running updated code to eventually overpower the attack.