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Sophos analysts are investigating a persistent, multi-stage malware distribution marketing campaign focusing on WhatsApp customers in Brazil. First noticed on September 24, 2025, the marketing campaign (tracked as STAC3150) delivers archive attachments containing a downloader script that retrieves a number of second-stage payloads. In early October, Counter Risk Unit™ (CTU) researchers detailed exercise related to a separate Brazil-based marketing campaign by which the menace actors leveraged WhatsApp to deploy the Maverick banking trojan for credential theft.

In STAC3150, the second-stage payloads embrace a script that collects WhatsApp contact data and session knowledge, and an installer that deploys the Astaroth (also called Guildma) banking trojan (see Determine 1).Determine 1: Assault chain within the WhatsApp STAC3150 marketing campaign

Assault development

The assaults begin with a message that’s despatched utilizing the WhatsApp “View As soon as” choice (see Determine 2).

Determine 2: WhatsApp lure (left) and translation (proper)

The lure delivers a ZIP archive that incorporates a malicious VBS or HTA file. When executed, this malicious file launches PowerShell to retrieve second-stage payloads, together with a PowerShell or Python script that collects WhatsApp person knowledge and, in later circumstances, an MSI installer that delivers the Astaroth malware. Determine 3 reveals the adjustments in downloader scripts and second-stage information over the course of the marketing campaign.

Determine 3: File codecs used within the STAC3150 marketing campaign between September 24 and October 31, 2025

In late September incidents, Sophos analysts noticed PowerShell getting used to retrieve the second-stage payloads by way of IMAP from an attacker-controlled e-mail account. In early October, the marketing campaign shifted to HTTP-based communication, leveraging PowerShell’s Invoke-WebRequest command to contact a distant command and management (C2) server hosted on https: //www . varegjopeaks . com (see Determine 4).

Determine 4: First-stage PowerShell instructions launched from malicious VBS file

The downloaded second-stage PowerShell or Python script (see Determine 5) makes use of the Selenium Chrome WebDriver and the WPPConnect JavaScript library to hijack WhatsApp Internet periods, harvest contact data and session tokens, and facilitate spam distribution.

Determine 5: PowerShell (left) and Python (proper) scripts for WhatsApp knowledge assortment

In late October, the second-stage information started to additionally embrace an MSI file (installer.msi) that delivers Astaroth malware.  The installer file writes information to disk and creates a startup registry key to keep up persistence. When executed, it launches the Astaroth malware by way of a malicious AutoIt script that masquerades as a .log file (see Determine 6). The malware communicates with a C2 server hosted at manoelimoveiscaioba . com.

Determine 6: AutoIt payload execution

Victimology

Sophos analysts noticed this marketing campaign affecting greater than 250 prospects, with roughly 95% of the impacted gadgets situated in Brazil. The remainder have been situated in different Latin American nations, the U.S., and Austria (see Determine 7).

Determine 7: Distribution of Sophos buyer gadgets impacted by the WhatsApp marketing campaign deploying Astaroth between October 23 and October 28, 2025

Suggestions, detections, and indicators

Organizations ought to educate staff concerning the dangers of opening archive attachments despatched by way of social media and prompt messaging platforms, even when acquired from recognized contacts.

SophosLabs has developed the countermeasures in Desk 1 to detect exercise related to this menace.

Desk 1: Sophos detections related to this menace

The menace indicators in Desk 2 can be utilized to detect exercise associated to this menace. The domains might comprise malicious content material, so take into account the dangers earlier than opening them in a browser.

Desk 2: Indicators for this menace