The ASEC analysis team has recently discovered a change in malicious PowerPoint files that are continually being distributed. As same as before, they use the method of executing a malicious script using mshta.exe, but added is the utilization of outlook.exe during the process.
Malicious PowerPoint files are being distributed as attachments of phishing e-mails as shown below, and they contain information related to purchase inquiries. Also, the malicious PowerPoint file is disguised as a PDF extension like in the previous type.
- Name of distributed file
When the malicious PowerPoint file is run, a security notice appears where the user selects whether or not to enable macros. Selecting Enable macros will run the malicious macro.
The malicious macro consists of simple codes, and it is automatically run by the Auto_Open() function. This variant contains a process of creating an Outlook application object via CreateObject(“Outlook.Application”) and executing the mshta command.
Ultimately, mshta is run by the outlook process, and the figure below is the process tree confirmed in RAPIT system.
The mshta command is identical to the previous version as it connects to the Blogspot website that includes a malicious script. Additional malicious behavior cannot be checked as this website has now been deleted, but various malware such as AgentTesla can be run depending on the malicious script.
- Malicious Command
- Final URL
It appears that the change in the method of running the malicious commands via the outlook.exe process is to bypass behavior detection.
As malicious PowerPoint files have been continually distributed via phishing mails since last year, users need to take extra caution when dealing with unidentified files. Users should also refrain from opening files from unknown sources or running suspicious macro included in the file.
[Previous Blog Posts about Malicious PowerPoint Files]
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