Fake Receipt Malspam Delivers GandCrab Ransomware Via Pdf Dropping Macro Dropping Exploit File

Office Macro Malware

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Following on from yesterday’s Dridex campaign, today is starting with another malspam campaign with emails with the subject of Receipt Feb-21310 [ random numbered] coming from random names @ cdkconstruction.org with a pdf attachment that in turn downloads a doc file that downloads ( or should download ) the malware payload which is the new GandCrab ransomware

The PDF today contacts & downloads http://butcaketforthen.com/docs/Feb-00974.doc. That drops a PowerShell script from the macro inside the doc. Now this is where it all goes pear shaped. The PowerShell script expressly calls the 32 bit version of PowerShell running a 64 bit computer. This means that a recipient running a 32 bit computer will not be infected. However to our detriment, it also means that the online sandboxes which run a 32 bit version of windows also won’t be able to get the malware payload.

Feb-9523713.pdf | VirusTotal |Anyrun Beta |
Feb-00974.doc Current Virus total detections: Hybrid analysis ( 32 bit version ) | HA (64 bit version) | Anyrun Beta | Cape Sandbox|

This malware doc downloads from http://sorinnohoun.com/sc1/sct5 ( VirusTotal) which gave me sct5 ( VirusTotal) This is a text file that appears to be some sort of exploit file that probably only works under windows 64 bit. I don’t think I have got the final GandCrab payload. There is probably something downloaded via the sct5 exploit file
Update: the payload is embedded as a base64 encoded section of the sct5 file which is a PowerShell commandlet file. That means it only runs via PowerShell and is effectively a fileless malware.

All the files are attached to this post in a zip ( P/W “infected” ) receipt
They use email addresses and subjects that will entice a user to read the email and open the attachment. A very high proportion are being targeted at small and medium size businesses, with the hope of getting a better response than they do from consumers.

One of the emails looks like:

From: Virgilio Stimson <Virgilio@cdkconstruction.org>
Date: Wed 07/02/2018 10:38
Subject: Receipt Feb-21310
Attachment: Feb-9523713.pdf

Body Content:

DOC attached

Screenshot:

These malicious attachments normally have a password stealing component, with the aim of stealing your bank, PayPal or other financial details along with your email or FTP ( web space) log in credentials. Many of them are also designed to specifically steal your Facebook and other social network log in details.

A very high proportion are Ransomware versions that encrypt your files and demand money ( about £350/$400) to recover the files.

All the alleged senders, amounts, reference numbers, Bank codes, companies, names of employees, employee positions, email addresses and phone numbers mentioned in the emails are all random. Some of these companies will exist and some won’t.

Don’t try to respond by phone or email, all you will do is end up with an innocent person or company who have had their details spoofed and picked at random from a long list that the bad guys have previously found. The bad guys choose companies, Government departments and organisations with subjects that are designed to entice you or alarm you into blindly opening the attachment or clicking the link in the email to see what is happening.
Please read our How to protect yourselves page for simple, sensible advice on how to avoid being infected by this sort of socially engineered malware.

Previous campaigns over the last few weeks have delivered numerous different download sites and malware versions. There are frequently 5 or 6 and even up to 150 download locations on some days, sometimes delivering the exactly same malware from all locations and sometimes slightly different malware versions. Dridex /Locky does update at frequent intervals during the day, sometimes as quickly as every hour, so you might get a different version of these nasty Ransomware or Banking password stealer Trojans.

This is another one of the files that unless you have “show known file extensions enabled“, can easily be mistaken for a genuine DOC / PDF / JPG or other common file instead of the .EXE / .JS file it really is, so making it much more likely for you to accidentally open it and be infected.

Be very careful with email attachments. All of these emails use Social engineering (https://en.wikipedia.org/wiki/Social_engineering_(security)) tricks to persuade you to open the attachments that come with the email. Whether it is a message saying “look at this picture of me I took last night” and it appears to come from a friend or is more targeted at somebody who regularly is likely to receive PDF attachments or Word .doc attachments or any other common file that you use every day.

The basic rule is NEVER open any attachment to an email, unless you are expecting it. Now that is very easy to say but quite hard to put into practice, because we all get emails with files attached to them. Our friends and family love to send us pictures of them doing silly things, or even cute pictures of the children or pets.

Never just blindly click on the file in your email program. Always save the file to your downloads folder, so you can check it first. Many malicious files that are attached to emails will have a faked extension. That is the 3 letters at the end of the file name.

Unfortunately windows by default hides the file extensions so you need to Set your folder options to “show known file types. Then when you unzip the zip file that is supposed to contain the pictures of “Sally’s dog catching a ball” or a report in word document format that work has supposedly sent you to finish working on at the weekend, or an invoice or order confirmation from some company, you can easily see if it is a picture or document & not a malicious program.

If you see JS or .EXE or .COM or .PIF or .SCR or .HTA .vbs, .wsf , .jse .jar at the end of the file name DO NOT click on it or try to open it, it will infect you.

While the malicious program is inside the zip file, it cannot harm you or automatically run. When it is just sitting unzipped in your downloads folder it won’t infect you, provided you don’t click it to run it. Just delete the zip and any extracted file and everything will be OK.

You can always run a scan with your antivirus to be sure. There are some zip files that can be configured by the bad guys to automatically run the malware file when you double click the zip to extract the file. If you right click any suspicious zip file received, and select extract here or extract to folder ( after saving the zip to a folder on the computer) that risk is virtually eliminated.

Never attempt to open a zip directly from your email, that is a guaranteed way to get infected. The best way is to just delete the unexpected zip and not risk any infection.

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