On Friday and Saturday, a chain reorganization occurred on the Litecoin network, rewinding approximately 32 minutes of activity after attackers exploited a vulnerability in the Mimblewimble Extension Block protocol. The attack allowed invalid transactions to bypass nodes that had not been updated, before the network's longest valid chain corrected them. The Litecoin Core v0.21.5.4 release contains important security updates and users are advised to upgrade. However, security researchers have pointed out discrepancies in the timeline of the patch, with the consensus vulnerability being privately patched between March 19 and 26, roughly four weeks before the attack.
The fix was rolled into release 0.21.5.4 after the attack had already begun. A separate denial-of-service vulnerability was patched on the morning of April 25. The exploit has raised concerns about the network's vulnerability to attacks and the need for more efficient patching and upgrading processes.
Blockchain data showed the attacker pre-funded a wallet 38 hours before the exploit and the destination address was configured to swap LTC into ETH on a decentralized exchange. The denial-of-service attack and the MWEB bug were separate components, with the DoS designed to take patched mining nodes offline so the unpatched ones would form the chain that included the invalid transactions. The network's automatic handling of the 13-block reorganization suggests that enough hashrate was running updated code to eventually overpower the attack. The incident highlights the differences in how code maintainers and developers react to exploits on various networks, with newer chains being more centralized and able to push patches network-wide in hours, while older proof-of-work networks like Litecoin rely on independent mining pools choosing when to upgrade.