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LummaStealer Returns to Scale as CastleLoader and 'ClickFix' Lures Drive New Wave

A Bitdefender report ties the resurgence to a stealthy in-memory loader using copy-paste CAPTCHA tricks following a 2025 takedown.

Overview

  • Bitdefender reports LummaStealer activity spiked in December 2025 and January 2026, with operations described as back at scale.
  • Recent campaigns frequently use CastleLoader, a heavily obfuscated AutoIt or Python script that runs payloads entirely in memory after sandbox checks.
  • ClickFix lure pages place malicious commands on the clipboard and instruct users to paste them into Windows Terminal, installing the loader that fetches Lumma.
  • Researchers highlight a detection clue in CastleLoader’s behavior: an intentional failed DNS lookup for a random, non-existent domain.
  • Distribution flows through trojanized and pirated downloads and lures on platforms such as Steam or Discord, despite a May 2025 seizure of about 2,300 Lumma domains.