Last week, researchers from the Microsoft Malware Protection Centre warned about a new wave of spam emails that carried malicious .LNK files inside ZIP archives. Those files had malicious PowerShell scripts attached to them.
PowerShell is a scripting language for automating Windows system administration tasks. It has been abused to download malware in the past and there are even malware programs written entirely in PowerShell.
In the recent campaign seen by Microsoft, the malicious LNK files contained a PowerShell script that downloaded and installed the Kovter click fraud trojan. The same technique has been used in the past to distribute the Locky ransomware.
On Thursday researchers from Intel Security warned that PowerShell can also be used in so-called fileless attacks, where the malicious code is launched directly into memory and nothing is saved to disk for endpoint security products to detect.
“You may think that you are protected from fileless malware because your PowerShell execution policies are set to ‘Restricted’ so that scripts can’t run,” the Intel Security researchers said in a blog post. “However, attackers can easily bypass these policies.”
Banning LNK or JS file attachments is easy, because it’s rare for people to send such files via email. However, banning SVG might prove impractical since it’s a widely used image format.