Litecoin Network Faces Denial-of-Service Attack, Successfully Reverses 13 Blocks

On Friday and Saturday, a series of events led to a 13-block chain reorganization on the Litecoin network, effectively rewinding 32 minutes of network activity. This was in response to an attack that exploited a vulnerability in the Mimblewimble Extension Block (MWEB) protocol, enabling a denial-of-service attack against major mining pools. The attackers took advantage of the fact that some nodes had not updated, allowing invalid MWEB transactions to slip through before the network's longest valid chain corrected them.

The Litecoin Core v0.21.5.4 release has since been made available, advising all users to upgrade due to important security updates. According to the Litecoin Foundation, the bug has been fully patched and the network is operating normally.

However, security researchers have pointed out discrepancies in the timeline of events, suggesting that the vulnerability was known and patched privately a month prior to the attack. The consensus vulnerability was privately patched between March 19 and March 26, and a separate denial-of-service vulnerability was patched on April 25. Both fixes were included in the release 0.21.5.4, which was rolled out 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 freedom to choose when to upgrade, creating a window of vulnerability in the event of a security patch.

In contrast, newer chains with smaller, more centralized validator sets can coordinate upgrades quickly and push patches network-wide in a matter of hours. The attack on Litecoin demonstrates how different networks respond to exploits, with the Litecoin Foundation's handling of the situation coming under scrutiny.

Blockchain data revealed that the attacker had pre-funded a wallet 38 hours before the exploit, with the destination address configured to swap LTC into ETH on a decentralized exchange. 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.

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.