On Friday and Saturday, a series of events led to a 13-block chain reorganization on the Litecoin network, effectively reversing approximately 32 minutes of network activity. This was in response to a denial-of-service attack that exploited a vulnerability in the Mimblewimble Extension Block protocol, allowing invalid transactions to bypass nodes that had not been updated. The Litecoin Core v0.21.5.4 release has been made available, and users are advised to upgrade due to important security updates. According to the Litecoin Foundation, the bug has been fully patched, and the network is now operating normally.
However, security researchers have pointed out discrepancies in the timeline of events, suggesting that the vulnerability was known and privately patched between March 19 and 26, roughly four weeks before the attack occurred. The consensus vulnerability was exploited to enable a denial-of-service attack against major mining pools, allowing invalid transactions to be processed before the network's longest valid chain corrected them. Prominent researchers, including those from the SEAL911 emergency response group for crypto exploits, have raised concerns about the handling of the incident, citing the privately patched vulnerability and the window of time where some miners were running patched code while others were still vulnerable. The attack has sparked discussions about the differences in how various networks respond to exploits, with newer chains often coordinating upgrades through chat groups and pushing patches network-wide in a matter of hours, whereas older proof-of-work networks like Litecoin rely on independent mining pools to choose when to upgrade, creating potential windows of vulnerability.