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Introduction
A silent cyberwar is unfolding across Brazil’s digital borders. What began as a familiar wave of banking‑trojan campaigns has rapidly mutated into something far more aggressive, more deceptive, and decidedly more modern. The threat actor known as Water Saci has rebuilt its entire machinery of infection—switching languages, upgrading delivery methods, and exploiting Brazil’s most trusted communication platforms. Their latest campaign blends PDFs, HTA files, Python scripts, and WhatsApp Web automation into a single, multi‑layered weapon designed to spread like wildfire. At its core lies a renewed determination to capture banking data from millions of unsuspecting users. Below is a full breakdown of how this campaign works, what makes it more dangerous than before, and why it signals a darker future for financial cybersecurity in Latin America.
Water Saci’s Expanding Attack Chain in Brazil
(30‑line human‑style summary of the original article)
A Growing Threat
Water Saci, a long‑observed Brazilian cybercrime group, has upgraded its infection strategy with a more complex workflow. The attackers now rely heavily on HTML Application files (HTA) and PDF attachments, both delivered through WhatsApp messages that appear to come from trusted contacts.
A Brand‑New Worming Approach
Instead of using older PowerShell‑based propagation methods, Water Saci has introduced a Python‑driven worm that automates malware delivery across WhatsApp Web. Researchers suspect that artificial intelligence tools may have helped translate parts of the PowerShell script into Python, as both versions share structure, logic, and even emoji‑tagged console messages.
Entrapment via Everyday Files
Victims encounter messages urging them to open what looks like an Adobe Reader‑related PDF or a supposed important HTA file. Once opened, the HTA variant executes a Visual Basic Script that triggers PowerShell commands to fetch additional stages: a malicious MSI installer and a Python script responsible for self‑propagation.
Multi‑Format Attacks with Increasing Resilience
Trend Micro analysts note that the Python version provides broader browser support, more stable execution, stronger error‑handling, and faster automated delivery through WhatsApp Web sessions. This evolution significantly boosts Water Saci’s ability to infect larger pools of victims in less time.
The MSI Dropper and AutoIt Loader
The MSI package installs a banking trojan delivered through an AutoIt script, which ensures only one active trojan instance is running by checking for a marker file called executed.dat. If missing, the file is created and reported to a command‑controlled server.
Language‑Aware Targeting
The trojan checks the infected system’s default Windows language and only proceeds with its full attack sequence if set to Portuguese (Brazil). It then scans the device for banking‑related folders associated with Brazil’s financial institutions, including Itaú, Bradesco, Caixa, and Sicoob.
Behavior Similar to Casbaneiro
Researchers highlight deep similarities between Water Saci’s trojan architecture and Casbaneiro, a notorious Latin American banking malware. These include AutoIt‑based delivery, window‑title monitoring, persistent Registry entries, and fallback IMAP‑based C2 channels.
Reconnaissance That Leaves No Room to Hide
The malware checks for antivirus tools, scrapes browser history for banking activity, harvests detailed system metadata, and constantly monitors open windows for banking‑related titles. When detected, it prepares to inject encrypted payloads into a hollowed svchost.exe process or load the banking trojan directly.
Persistence Through Process Monitoring
If the trojan’s injected process is terminated, Water Saci restarts the attack flow and waits until the victim opens another financial window, ensuring the infection remains active.
Aggressive Anti‑Detection Behavior
Once launched, the trojan performs extensive anti‑virtualization checks, collects host data, and connects to a remote C2 server to receive commands that allow attackers to remotely control the device. Functions include keylogging, screen capture, file manipulation, and fake banking overlays.
Automated WhatsApp Worming via Selenium
A Python script powered by Selenium allows the malware to send infected attachments to every WhatsApp Web contact, turning victims into unwilling spreaders of the attack.
A Parallel Threat: RelayNFC Malware
Alongside Water Saci, Brazilian users now face another danger: RelayNFC, a novel Android malware designed to conduct real‑time NFC relay attacks and steal contactless payment data. Built in React Native, it complicates analysis and avoids detection.
Phishing as the First Step
RelayNFC spreads through fake Portuguese‑language security sites urging users to “protect” their payment cards. Once installed, the malware collects card data through NFC taps and transmits it to attackers using WebSockets.
An Alarming Evolution in Payment Fraud
The malware can forward APDU commands between the victim’s phone and an attacker’s POS emulator, allowing fraudsters to perform real‑time purchases as if they physically held the victim’s card. Evidence also shows experiments with Host Card Emulation (HCE) to enhance future attacks.
What Undercode Say:
(40‑line expert analysis)
A Campaign That Reveals the Future of Brazilian Cybercrime
Water Saci’s new strategy represents not just an upgrade—but a transformation. The shift from PowerShell to Python isn’t a cosmetic rewrite. It signals a threat actor that understands scalability, automation, and platform reach. Python allows for cross‑browser stability, easier extension, and a more flexible architecture for worm‑style propagation. For a WhatsApp‑driven campaign, that’s a multiplier effect. Every victim becomes a broadcasting node.
Weaponizing Trust
Brazil’s digital culture is deeply rooted in WhatsApp communication. Family, co‑workers, banks, and businesses all rely heavily on the platform. Water Saci abuses this trust by pushing malware through contacts people inherently believe. The victim is deceived not by a faceless attacker, but by the digital echo of someone they know.
A Multi‑Layered Infection That Costs Little but Yields Much
This attack chain is not costly to operate. PDFs and HTA files are lightweight. AutoIt remains one of the easiest loaders to modify. Python and Selenium provide automation without complexity. The sophistication is not in the tools but in how they’re combined—and in the psychology of the user journey.
Targeting Brazil’s Banking DNA
Brazil’s banking ecosystem is heavily digitized, even more than many Western regions. This creates a large attack surface. Water Saci’s decision to target Portuguese‑language systems and scan for specific banking apps shows clear focus: this is not a global campaign, but a surgical one.
Casbaneiro Legacy, New Techniques
The similarities to Casbaneiro are not accidental. Water Saci is either inspired by, borrowing from, or collaborating with developers connected to older LATAM banking trojans. The way the malware monitors window titles, interacts with Registry keys, and decrypts staged payloads points to shared lineage.
AI‑Assisted Malware Development Is No Longer Theoretical
The presence of emojis in Python console output, matching the PowerShell structure, hints at code converted using LLM‑based tools. This is a critical turning point. AI‑assisted cybercrime means faster development cycles, easier refactoring, and near‑instant portability across languages.
RelayNFC Is Proof That Payment Fraud Is Entering a New Era
While Water Saci focuses on desktop banking, RelayNFC pushes into mobile payment fraud. Real‑time APDU relaying is not amateur work; it requires knowledge of EMV protocols and POS behavior. Combined with React Native obfuscation and phishing infrastructure, Brazil is now facing threats across both traditional and contactless payment channels.
A Dual‑Front Battle
Brazilian users are now under attack from both sides:
• Desktop malware stealing banking credentials
• Mobile malware stealing NFC payment data
Both are delivered through social engineering. Both rely on user behavior. And both are rapidly evolving.
The Bigger Picture
This campaign symbolizes a new operational standard for LATAM cybercrime groups: multi‑channel infection, AI‑assisted development, banking‑specific reconnaissance, and platform‑agnostic propagation. If unaddressed, these techniques will inevitably spread beyond Brazil into broader global ecosystems.
Fact Checker Results
Water Saci’s new malware chain: Verified. Trend Micro researchers confirm the shift from PowerShell to Python. ✅
WhatsApp Web used for worm‑style propagation: Accurate, observed directly in the research. ✅
RelayNFC Android malware with real‑time APDU relaying: Confirmed in Cyble’s analysis. ✅
Prediction
Water Saci will likely expand its targeting beyond Brazil, evolving into a regional LATAM threat as attackers reuse the Python‑based infrastructure and WhatsApp worming system. 📌
Future variants may integrate mobile trojans to synchronize desktop and smartphone infections, creating hybrid campaign models. 📌
Payment‑card relay malware like RelayNFC will continue to grow, driven by Brazil’s rapid adoption of digital wallets and contactless payments. 📌
🕵️📝✔️Let’s dive deep and fact‑check.
References:
Reported By: thehackernews.com
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