A chain reorganization occurred on the Litecoin network late Friday and Saturday, undoing approximately 32 minutes of network activity. This was in response to an attack leveraging a vulnerability in its Mimblewimble Extension Block (MWEB) protocol, allowing for a denial-of-service attack against major mining pools. The bug enabled invalid MWEB transactions to bypass nodes that had not been updated, before the network's longest valid chain corrected them. Following the incident, 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 resumed normal operation by Sunday morning. However, security researchers point out that the timeline of events, as indicated by the litecoin-project GitHub repository, suggests the vulnerability was known and privately patched between March 19 and 26, roughly four weeks prior to the attack. This created a window of vulnerability where some miners ran the patched code while others continued to run the vulnerable version, which the attackers seemed to be aware of. The consensus vulnerability and a separate denial-of-service vulnerability were both rolled into the release 0.21.5.4 after the attack had begun.
The exploit highlights the challenges faced by older proof-of-work networks like Litecoin, where independent mining pools have the discretion to choose when to upgrade, potentially creating a window of vulnerability in the case of urgent security patches. The full extent of the attack, including the amount of LTC pegged out during the invalid block window and the value of any swaps completed before the reorganization, has not been disclosed.