The following detection identifies the module load of mshtml.dll into an Office product. This behavior has been related to CVE-2021-40444, whereas the malicious document will load ActiveX, which activates the MSHTML component. The vulnerability resides in the MSHTML component. During triage, identify parallel processes and capture any file modifications for analysis.
- Type: TTP
- Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- Datamodel: Endpoint
- Last Updated: 2021-09-09
- Author: Michael Haag, Splunk
- ID: 5f1c168e-118b-11ec-84ff-acde48001122
|T1566.001||Spearphishing Attachment||Initial Access|
`sysmon` EventID=7 process_name IN ("winword.exe","excel.exe","powerpnt.exe","mspub.exe","visio.exe","wordpad.exe","wordview.exe") ImageLoaded IN ("*\\mshtml.dll", "*\\Microsoft.mshtml.dll","*\\IE.Interop.MSHTML.dll","*\\MshtmlDac.dll","*\\MshtmlDed.dll","*\\MshtmlDer.dll") | stats count min(_time) as firstTime max(_time) as lastTime by Computer, process_name, ImageLoaded, OriginalFileName, process_id | rename Computer as dest | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `mshtml_module_load_in_office_product_filter`
Associated Analytic Story
How To Implement
To successfully implement this search, you need to be ingesting logs with the process names and image loads from your endpoints. If you are using Sysmon, you must have at least version 6.0.4 of the Sysmon TA.
Kill Chain Phase
Known False Positives
Limited false positives will be present, however, tune as necessary.
|80.0||80||100||An instance of $process_name$ was identified on endpoint $dest$ loading mshtml.dll.|
|CVE-2021-40444||Microsoft MSHTML Remote Code Execution Vulnerability||6.8|
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