Active Email Campaign Identified With Malicious Excel Files
We identified a potential campaign in preparation where the victim would received a zip file containing a Malicious Excel file embedding Excel 4.0 Macros — requiring user interaction to infect the victim.
The chain works as the following:
- Victim receives a compressed archive (.xls.zip) file.
- Once opened, the .xls file asks the user to enable macros to allow the document to connect to a remote server to send a web request that return back the malicious macros to be executed. This is quiet ingenious as it allows some degree of flexibility to the attacker — but also to evade traditional detection since the malicious macros would not be inside the file.
- Malicious macro downloads a dll which gets executed with
regsvr32
- Weirdly enough, the dll that gets downloaded is a 32-bits dll which WinExec() Windows’s Calculator application.
We found that the distributing domains are hosted on Alibaba Cloud. Details are provided at the end of the blog-post. Domains were registered on Feb 7, 2020 and Feb 10, 2020.
It is unclear at this point if the attackers are just doing some scoping & testing on an upcoming campaign.
The shellcode is pretty much an exact copy of a shellcode available on GitHub: which is a modified version of a 10 years old shellcode’s w32-bind-ngs-shellcode by another researcher.
This could be that attackers are in training and learning how to spam and infect victims, or also that those servers will be rotated with more malicious contents. It is also unclear if this campaign is connected to Dudear.
Key Recommendations:
- Do not enable macros on files from unknown senders
- Always be suspicious of legacy office files such as .XLS, .DOC or .RTF.
- Make sure to have memory analysis as part of your incident response strategy to detect and assess potential infections on hosts. We can help you with our automated platform and utilities.
- Consider using Application Guard for Microsoft Office.
- Follow us on Twitter / LinkedIn to stay informed about emerging campaigns and techniques.
Indicator of compromise (IoC):
Excel File Hashes
95A90C0B8EC19142BF8BB125DDAABCFFE8D2CE41C6FD6A0836AD8F47C3CEA693
9F2439791D0773BE5E29730294F4635A3BAC4A0D3D1D537AAB5F9E8801C4281F
25F63735898AEFD98B8F9F9CD5E7F725B5A0E6626A65AD3AA2875E56B8AF6C09
47AA7E92B26278ED656ACEAE21DB6C6877C7A006E38F0E95F85EA07C99787E0B
Malicious DLL
85697BFC0E89C5499A46AEEC656B3B9FACD8B9FE7174B3DB9B2B9F7DBCBAAEDB
Domain Names & Servers:
Domains are sharing a common IP address, and to are hosted in Alibaba Cloud.
veqejzkb.xyz (Registered On 2020-02-10)
merystol.xyz (Registered On 2020-02-07)
161.117.177.248