The Gamaredon threat group has built a post-compromise tool arsenal that includes remote template injectors for Word and Excel documents as well as a unique Outlook mass-mailing macro, researchers recently discovered.

The tools, previously undocumented, boast a VBA macro aimed at Outlook that sends spearphishing emails to a victim’s Microsoft address book contacts, according to ESET researchers. Noting that the Gamaredon-linked tools were “detected as variants of MSIL/Pterodo, Win32/Pterodo or Win64/Pterodo,” ESET said in a blog post that the threat group, known for attacks mostly against Ukrainian organizations, has upped its activities “with constant waves of malicious emails hitting their targets’ mailboxes.”

The VBA employs a bundle of malicious code starting with a VBScript that kills the Outlook process then changes registry values to remove security around VBA macro execution in Outlook. The malicious OTM file containing a macro, the malicious email attachment and, sometimes, a list of recipients for the email are saved to disk. Once Outlook is relaunched with a special option that loads the Gamaredon VBA project, and after the Application.Startup event is received, malicious code is executed, sending malicious email to either everyone in a victim’s address book or within an organization or to predefined targets.

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