Oh look, an unsolicited incoming Fax Report. Odd it is a fax transmission, but our company doesn’t even have a fax server. But it is on 2013 Recruitment Planning – I better open it!
Corporate networks are being slammed with e-mails like the one above. Looks innocent enough, but if a user did indeed open it, the malicious attachment that anti-virus didn’t detect would scan the victim’s hard drive for data and upload it to a malicious server. All undetected by the unsuspecting user.
I have seen several versions of this same attack in the last week. So let’s take a closer look.
When these attacks first started, only 2 anti-virus engines would detect the attachment as a malicious file. AV engines are catching on to it now and are detecting it as a generic Trojan. As a matter of fact, if I try to open this message today, I get a message from Microsoft Mail that the attachment is malicious:
So let’s take a closer look at one of these “Incoming Fax Report” attachments.
*** WARNING: Never open suspected malware on a live, network connected system. In this example I use a sandboxed virtual memory system running with very limited network capabilities. ***
The attachment, once unzipped, shows a PDF icon, but this is no PDF file. The file has an .exe extension meaning that the file is an executable and not a text file. So how can we take a closer look at the program to see what it does?
The program Dependency Walker will show us what functions that the program uses and will give us a clue as to what the program actually does. If we run Dependency Walker we can see the .dll files that the program calls and what main functions it uses:
Okay, it may not be very clear from the Kernel32 side, but you can see this program uses functions like CreateFile, DeleteFile, GetCurrentDirectory, GetEnvironmentVariable. It is definitely poking around the file system.
And if you look at the functions under Wininet.dll you see a whole bunch of FTP commands:
Any guesses on where this is going?
Now that we have a general idea of what it could do, let’s execute it in a controlled environment so we can see what it actually does. We will want to know what registry settings it touches, what network communication is attempted and as much about the running processes as we can obtain.
For this we will use the following programs:
Regshot is very easy to use, just download and run it. You then have three options. 1st Shot, 2nd Shot and Compare. Simply select 1st Shot to get a baseline look at your registry. Then Run the suspicious program. Next hit 2nd Shot to capture any changes made to your registry.
Finally select Compare to get a report of any changes made:
Process Monitor is a bit more involved. Basically after you run it, you need to turn off capturing (File, then uncheck Capture Events) and clear the cache (Edit, then Clear Display). Leave the capturing off until you are ready to fire up the malware. Then turn capturing on and execute the malware.
Let it run for a few minutes then you can turn off capturing so you don’t fill your system memory up with process captures.
Then finally we need to Filter for our suspicious file. So select Filter, then Filter again. Then select Process Name from the first drop down box, Leave “is” in the second box, then pick the filename of the file you want to monitor in the third box:
Then just click “Add” and “OK”.
You can now view all the process information that is related to the malicious file.
You can further filter the data available for the file in question by using the 5 select boxes on the menu:
With these you can view just registry activity, processes, file use activity , network use, etc.
If we look at our malicious file with Process Monitor you will see that the program searches your entire drive for user files, installed programs, security programs and patches, Installed FTP programs, file manager programs and even remote storage clients (like Dropbox).
Finally we want to see what network activity the virus initiates. Simply have Wireshark running before you execute the program.
As you can see, as soon as the malware was executed, it immediately tries to connect out to a malicious server.
As you can see if a user is duped into allowing the malicious e-mail attachment to run, a basic analysis of the file shows that it is a data miner trojan. It searches your hard drive for all data that could be of interest then tries to send it out to a malicious server.
Of the three different samples obtained. All were similar in that they claimed to be a fax report from an internal fax server. Some looked much more believable than others. All three had an executable attachment that was masked to look like a .pdf file.
All three searched the hard drive and registry for pertinent information. And all three connected out to a suspicious server address. The funny thing is that when all three were run through the Who-is Database, all three domains pointed to the same server!
Lastly the e-mail addresses in all three seemed to be in a somewhat alphabetical order. This seems to point to a botnet type control system going through a list of e-mail addresses, breaking them down into a groups and sending them one of the malicious e-mails.
These type of automated phishing attacks are becoming very common. The best line of defense against these attacks are vigilant users who question unsolicited e-mails, especially ones with attachments. Blocking incoming and outgoing IPs from unneeded locations and ingress and egress filtering is paramount in stopping these attacks.
Network Security Monitoring with full packet capture will also help to find what, if any, data was actually compromised if the attack is a success.
This was just a very basic analysis of this malicious attachment. Want to take a closer look at these techniques and learn a whole lot more about malware analysis including advanced techniques? Check out Practical Malware Analysis: The Hands-On Guide to Dissecting Malicious Software by Michael Sikorski and Andrew Honig.