On Friday and Saturday, a series of events unfolded as a denial-of-service attack hit Litecoin, leveraging a vulnerability in its Mimblewimble Extension Block (MWEB) protocol to temporarily disrupt the network. Approximately 32 minutes of network activity were rewound following a 13-block chain reorganization, which occurred at an LTC price of $55.31. The exploit allowed invalid MWEB transactions to bypass nodes that had not been updated, prior to the network's longest valid chain correcting them. In response, Litecoin Core v0.21.5.4 was released, advising all users to upgrade due to important security updates.
According to the Litecoin Foundation, the bug was fully patched and the network returned to normal operation by Sunday morning. However, security researchers have pointed out discrepancies in the timeline of events, suggesting that the consensus vulnerability was known and privately patched between March 19 and 26, roughly four weeks before the attack occurred. This raised concerns about the window of vulnerability created when not all mining pools had updated their code, potentially allowing attackers to exploit the gap. The incident highlights the differences in how various networks respond to exploits, with newer chains capable of coordinating upgrades quickly and older proof-of-work networks like Litecoin facing challenges in rapidly implementing security patches across independent mining pools.