Top Highlights
- The Guildma malware infection utilized geo-fenced malicious links delivered via targeted Brazilian Portuguese phishing emails, exploiting regional and language settings to evade detection.
- The malware employed a ZIP archive containing a Windows shortcut that retrieved and executed a DLL, establishing persistence and command-and-control communication over HTTPS with specific domain infrastructure.
- Unique SHA-256 hashes for the malware components and custom AutoIt scripts suggest targeted, sophisticated threat activity focused on persistent infection and data exfiltration.
Threat Overview, Techniques, and Targets
The threat involves a Guildma (Astaroth) malware infection. It begins when a user clicks a specially crafted link in a Brazilian Portuguese email. This link is geofenced to only deliver malicious content if the user IP is from Brazil. If not, the email shows a legitimate installer. The email’s headers and content suggest the attack aims to target users in Brazil.
The malware delivery starts with a ZIP archive containing a Windows shortcut. When opened, the shortcut downloads content from a remote server and saves it as an alternate data stream in the Temp folder. A DLL file found in the stream is not malicious on its own. However, it is used to retrieve and install AutoIt scripts that activate the Guildma malware. The malware also makes encrypted HTTPS connections to various domains, including Azure web services and other Cfd domains.
The attack relies on social engineering through the email. It also uses geofencing and language/region settings to make sure only users in Brazil become infected. The infection targets Windows hosts in particular, using layered downloads and native Windows features to hide the activity.
Impact, Security Implications, and Remediation Guidance
This malware can cause serious harm. Once infected, an attacker can gain persistent access to the compromised Windows system. The malware communicates with remote servers to update or manage the infection. This communication can lead to data theft or further malware downloads.
The infection also demonstrates how localized and obfuscated cyber attacks can be. Using geofencing and language-specific settings makes detection harder. Security teams should be alert for similar emails and suspicious activity. The network traffic to specific Azure domains and unusual files in Temp folders are key indicators.
If a device is suspected to be infected, remediation guidance should be obtained directly from the relevant security vendor or authority. It is crucial to isolate the affected system immediately. Conduct a full malware scan using reputable security tools. Remove any suspicious files, especially those related to the observed DLL and AutoIt scripts. Review network logs for ongoing communication with malicious domains. As always, keeping systems and security software updated is recommended to prevent similar attacks.
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