Late Friday and Saturday, a series of events unfolded as a 13-block reorganization occurred on the Litecoin network, effectively rewinding 32 minutes of network activity. This was a response to an attack that leveraged a vulnerability in the Mimblewimble Extension Block (MWEB) protocol, enabling a denial-of-service attack against major mining pools and allowing invalid MWEB transactions to temporarily go through. The Litecoin Core v0.21.5.4 release, which includes crucial security updates, has been made available, with all users advised to upgrade.
According to the Litecoin Foundation, the bug has been fully patched, and the network is now operating as normal. However, security researchers have pointed out discrepancies in the timeline of events, citing the litecoin-project GitHub repository, which indicates the consensus vulnerability was known and privately patched between March 19 and 26, approximately four weeks before the attack took place. A separate denial-of-service vulnerability was patched on April 25.
Both fixes were incorporated into release 0.21.5.4 on the afternoon of the attack. The term 'zero-day' refers to a vulnerability that is unknown to the defenders at the time of the attack.
The consensus vulnerability, which allowed for an invalid MWEB peg-out, was privately addressed a month before the exploit but had not been publicly disclosed or mandated for all mining pools. This created a window of opportunity where some miners were running the patched code, while others were still using the vulnerable version, and it appears the attackers were aware of this distinction. Concerns have been raised by various experts, including Alex Shevchenko, CTO of NEAR Foundation's Aurora project, who highlighted the pre-funding of a wallet 38 hours before the exploit and the subsequent configuration to swap LTC for ETH on a decentralized exchange.
Shevchenko argued that the denial-of-service attack and the MWEB bug were separate components, with the DoS designed to take patched mining nodes offline, thereby allowing the unpatched ones to form a chain that included the invalid transactions. The automatic handling of the 13-block reorganization by the network once the DoS stopped suggests that enough hashrate was running updated code to eventually overpower the attack, albeit after the unpatched fork had run for 32 minutes. This incident highlights the differences in how attacks on various networks are handled, particularly in terms of code maintainers and developers reacting to exploits. Newer chains with smaller, more centralized validator sets can coordinate upgrades quickly, while older proof-of-work networks like Litecoin and Bitcoin rely on independent mining pools choosing when to upgrade, which can create a window of vulnerability when a security patch needs to be implemented before an attacker exploits it.
As of Sunday morning, the Litecoin Foundation has not publicly addressed the GitHub timeline, and the amount of LTC pegged out during the invalid block window, as well as the value of any swaps completed before the reorganization reversed them, have not been disclosed.