Documents with malicious macros deliver fileless malware to financial-transaction systems

Attackers are using Word documents with malicious macros and PowerShell to infect computers with fileless malware, researchers warn

Spammed Word documents with malicious macros have become a popular method of infecting computers over the past few months. Attackers are now taking it one step further by using such documents to deliver fileless malware that gets loaded directly in the computer's memory.

Security researchers from Palo Alto Networks analyzed a recent attack campaign that pushed spam emails with malicious Word documents to business email addresses from the U.S., Canada and Europe.

The emails contained the recipients' names as well as specific information about the companies they worked for, which is not typical of widespread spam campaigns. This attention to detail lent more credibility to spam messages and made it more likely that victims would open the attached documents, the researchers said.

The documents contained macros that, if allowed to run, execute a hidden instance of powershell.exe with special command-line arguments. Windows PowerShell is a task automation and configuration management framework that's included in Windows by default and comes with its own scripting language.

The PowerShell command executed in this case was designed to check if the Windows OS was a 32-bit or a 64-bit version and to download an additional PowerShell script that corresponded to the OS architecture.

The rogue script performs a variety of checks on the computer. First it tries to determine if the environment is a virtual machine or sandbox like those used by malware analysts. It then scans the network configuration for strings like school, hospital, college, health and nurse. It also scans the network for other machines with names including teacher, student, schoolboard, pediatrics, orthoped, as well as POS, store, shop and sale. Cached URLs are scanned for a number of financial websites and names like Citrix and XenApp.

According to the Palo Alto researchers, the goal of these checks is to find systems that are used to conduct financial transactions and to avoid systems that belong to security researchers as well as medical and educational institutions.

Only systems that match what the attackers are looking for are flagged and reported back to a command-and-control server. For those systems, the script downloads a malicious encrypted DLL (dynamic link library) file and load it into memory.

"Due to the target-specific details contained within the spam emails and the use of memory-resident malware, this particular campaign should be treated as a high threat," the Palo Alto researchers said in a blog post.

A similar combination of PowerShell and fileless malware was observed last week by researchers from the SANS Institute's Internet Storm Center.

That malware creates a registry key that launches a hidden PowerShell instance at every system start-up. The PowerShell command executes an encoded script that's stored in a separate registry key. Its goal is to decrypt and load an executable file directly into memory without ever writing it to disk.

"By using PowerShell the attackers have been able to put malware that might otherwise be detected on a hard drive into the Windows Registry," senior SANS instructor ​Mark Baggett, said in a blog post.

Storing malicious code in the system registry, abusing the Windows PowerShell and adding malicious macros to documents are not new techniques. However, their combination can make for very potent and hard-to-detect attacks.

Join the newsletter!

Or

Sign up to gain exclusive access to email subscriptions, event invitations, competitions, giveaways, and much more.

Membership is free, and your security and privacy remain protected. View our privacy policy before signing up.

Error: Please check your email address.
Keep up with the latest tech news, reviews and previews by subscribing to the Good Gear Guide newsletter.

Lucian Constantin

IDG News Service
Show Comments

Cool Tech

Toys for Boys

Family Friendly

Stocking Stuffer

SmartLens - Clip on Phone Camera Lens Set of 3

Learn more >

Christmas Gift Guide

Click for more ›

Brand Post

Most Popular Reviews

Latest Articles

Resources

PCW Evaluation Team

Aysha Strobbe

Microsoft Office 365/HP Spectre x360

Microsoft Office continues to make a student’s life that little bit easier by offering reliable, easy to use, time-saving functionality, while continuing to develop new features that further enhance what is already a formidable collection of applications

Michael Hargreaves

Microsoft Office 365/Dell XPS 15 2-in-1

I’d recommend a Dell XPS 15 2-in-1 and the new Windows 10 to anyone who needs to get serious work done (before you kick back on your couch with your favourite Netflix show.)

Maryellen Rose George

Brother PT-P750W

It’s useful for office tasks as well as pragmatic labelling of equipment and storage – just don’t get too excited and label everything in sight!

Cathy Giles

Brother MFC-L8900CDW

The Brother MFC-L8900CDW is an absolute stand out. I struggle to fault it.

Luke Hill

MSI GT75 TITAN

I need power and lots of it. As a Front End Web developer anything less just won’t cut it which is why the MSI GT75 is an outstanding laptop for me. It’s a sleek and futuristic looking, high quality, beast that has a touch of sci-fi flare about it.

Emily Tyson

MSI GE63 Raider

If you’re looking to invest in your next work horse laptop for work or home use, you can’t go wrong with the MSI GE63.

Featured Content

Don’t have an account? Sign up here

Don't have an account? Sign up now

Forgot password?