Security researchers identified a malspam campaign targeting Italian users with a variant of the sLoad downloader.
In October and November, CERT-Yoroi detected a series of malicious email messages that shared common techniques. Each malicious sample arrived as a compressed ZIP archive containing two files: an LNK file pretending to point to a system folder and a hidden JPEG image stored with HA attributes.
When a user clicks on the link, the file uses a batch script to run a PowerShell script, which searches for another ZIP file. If it exists, the PowerShell script extracts code from that file and uses it to download other scripts. Among those other scripts are “NxPgKLnYEhMjXT.ps1,” which installs the sLoad implant on the victim’s machine.
Successful execution enables sLoad to collect information about the infected computer and periodically capture screenshots, among other functionality. It then sends this data to attackers via command and control (C&C) channels before receiving additional PowerShell code, behavior that is characteristic of Trojans and spyware.
sLoad: The Latest PowerShell-Borne Threat
This isn’t the first time that security researchers have detected attacks utilizing sLoad. In May 2018, the SANS Internet Storm Center (ISC) identified a PowerShell script targeting customers of major U.K. banks. Further analysis tied this activity to hxxps://cflfuppn[.]eu/sload/run-first.ps1.
Together, these campaigns targeting Italian and U.K. users represent the latest activity of just one threat delivered by PowerShell scripts. IBM X-Force Incident Response and Intelligence Services (IRIS) observed an increase in PowerShell attacks between 2017 and 2018. This finding coincides with Symantec’s detection of a 661 percent increase in the number of computers registering blocked PowerShell activity between mid-2017 and mid-2018.
How Security Professionals Can Block a Malspam Campaign
Security professionals can help defend their organizations against malspam campaigns by investing in awareness training that instructs employees to avoid suspicious links and email attachments. IBM X-Force IRIS also recommends using physical security controls to block the abuse of PowerShell scripts, and integrating security information and event management (SIEM) and endpoint detection and response (EDR) tools to provide an additional layer of protection.
Sources: Yoroi, SANS ISC, Symantec
David Bisson is an infosec news junkie and security journalist. He works as Contributing Editor for Graham Cluley Security News and Associate Editor for Trip...