GootLoader Employs Malformed ZIPs to Bypass Detection
🛡️ Expel researchers report that the JavaScript loader GootLoader is using deliberately malformed ZIP archives — concatenating 500–1,000 archives and truncating the EOCD — to evade analysis while remaining extractable by the default Windows unarchiver. The technique, described as hashbusting, ensures each archive is unique and frustrates automated tooling like WinRAR or 7-Zip. Distribution relies on SEO poisoning and malvertising, and the payload executes via wscript.exe, establishing persistence and launching PowerShell activity. Recommended mitigations include blocking wscript.exe/cscript.exe for downloaded content and configuring Group Policy to open .js in Notepad by default.
