Litecoin has issued a critical security update with the release of Core version 0.21.5.5, addressing a zero-day vulnerability that previously led to a denial-of-service attack. The update includes significant MWEB consensus enhancements, improved node reliability, and fixes for wallet and mining operations. All node operators and wallet users are urged to upgrade immediately to ensure network security. The vulnerability, discovered in March 2026, affected the Mimblewimble extension block implementation, allowing invalid transactions that caused a 13-block reorganization. The new update increases the maximum length of P2P protocol messages to 32 MB and resolves issues related to MWEB validation, state handling, and transaction index consistency. The Litecoin team has also improved tests for various network functions to prevent future incidents.