Proofpoint researchers have recently detected the reappearance of threat actor TA866 in a significant email threat campaign, marking the end of a nine-month absence. On January 11, 2024, Proofpoint successfully thwarted a large-scale campaign aimed at North America, involving several thousand emails. The attackers utilized invoice-themed emails, each housing PDF attachments named “Document_[10 digits].pdf,” with subjects such as “Project achievements.”
The PDFs contained OneDrive URLs, initiating a complex infection chain upon clicking, ultimately leading to the deployment of a malware payload, specifically a variant of the WasabiSeed and Screenshotter custom toolset. The attack chain mirrored similarities with TA866’s last documented campaign on March 20, 2023, utilizing the TA571 spam service and maintaining consistency in the WasabiSeed downloader and Screenshotter scripts. However, a notable change was the introduction of a PDF attachment containing a OneDrive link, deviating from previous campaigns that utilized macro-enabled Publisher attachments or 404 TDS URLs directly in the email body.
Attribution of the threat actors reveals that TA571, a spam distributor, handled the delivery service for the malicious PDF, while TA866, known for engaging in both crimeware and cyberespionage activities, managed the post-exploitation tools. The campaign’s financial motivation raises concerns, emphasizing TA866’s organized capabilities in executing well-thought-out attacks at scale, with access to custom tools and connections to purchase additional services from other threat actors.
