Late Friday and Saturday, a chain reorganization of 13 blocks on the Litecoin network reversed approximately 32 minutes of activity. This was in response to an attack that exploited a vulnerability in the Mimblewimble Extension Block (MWEB) protocol, allowing invalid transactions to bypass nodes that had not yet updated.
The Litecoin Core v0.21.5.4 release, which includes crucial security updates, has been made available, and all users are advised to upgrade. According to the Litecoin Foundation, the bug has been fully patched, and the network is now operating normally.
However, some researchers have pointed out discrepancies in the timeline of events, as indicated by the litecoin-project GitHub repository. The repository shows that the consensus vulnerability was privately patched between March 19 and 26, roughly four weeks before the attack occurred. A separate denial-of-service vulnerability was patched on the morning of April 25, and both fixes were included in the release 0.21.5.4 the same afternoon, after the attack had begun. The term 'zero-day' refers to a vulnerability that is unknown to defenders at the time of an attack.
In this case, the consensus vulnerability was known and patched privately a month before the exploit but had not been publicly announced or mandated for all mining pools. This created a window of opportunity for attackers, who seemed to be aware of which miners were running the patched code and which were still vulnerable. Alex Shevchenko, CTO of NEAR Foundation's Aurora project, has raised concerns about the exploit, highlighting that blockchain data showed the attacker had pre-funded a wallet 38 hours before the exploit through a Binance withdrawal.
The destination address was already set up 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, allowing the unpatched ones to form a chain that included the invalid transactions. The fact that the network automatically handled the 13-block reorganization once the DoS stopped suggests that enough hashrate was running updated code to eventually overpower the attack. However, this only occurred after the unpatched fork had run for 32 minutes.
The incident highlights how attacks on different networks can vary in terms of how code maintainers and developers respond to exploits. Newer chains with smaller, more centralized validator sets can coordinate upgrades through chat groups and push patches network-wide in hours. In contrast, 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 reach everyone before an attacker exploits the gap.
As of Sunday morning, the Litecoin Foundation had not publicly addressed the GitHub timeline. The amount of LTC pegged out during the invalid block window and the value of any swaps completed before the reorganization reversed them have not been disclosed.