On Friday and Saturday, a series of events unfolded as a 13-block chain reorganization occurred on the Litecoin network, effectively rewinding 32 minutes of network activity. This was in response to an attack that leveraged a vulnerability within the Mimblewimble Extension Block (MWEB) protocol, allowing for the execution of a denial-of-service attack against major mining pools. The attack enabled the processing of invalid MWEB transactions, which were later corrected by the network's longest valid chain.
In the aftermath, Litecoin Core v0.21.5.4 was released, containing crucial security updates. The Litecoin Foundation announced that the bug had been fully patched and the network was operating normally by Sunday morning.
However, security researchers have pointed out discrepancies in the timeline of events, suggesting that the vulnerability was known and patched privately a month before the attack. The consensus vulnerability was patched between March 19 and 26, while a separate denial-of-service vulnerability was addressed on April 25.
Both fixes were incorporated into the release 0.21.5.4 after the attack had begun. The incident highlights the challenges faced by older proof-of-work networks like Litecoin, where independent mining pools have the autonomy to choose when to upgrade, creating potential windows of vulnerability.
Prominent researchers, including Alex Shevchenko, CTO of NEAR Foundation's Aurora project, have raised concerns about the attack, suggesting that it was a coordinated effort involving a denial-of-service attack designed to take patched mining nodes offline, allowing the inclusion of invalid transactions. The fact that the network was able to automatically handle the 13-block reorganization once the DoS stopped indicates that a sufficient amount of hashrate was running updated code to eventually overpower the attack.