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Description

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

Annotations

ATT&CK
ID Technique Tactic
T1566 Phishing Initial Access
T1566.001 Spearphishing Attachment Initial Access
Kill Chain Phase
  • Exploitation
NIST
CIS20
CVE
ID Summary CVSS
CVE-2021-40444 Microsoft MSHTML Remote Code Execution Vulnerability 6.8
1
2
3
4
5
6
`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`

Macros

The SPL above uses the following Macros:

Note that mshtml_module_load_in_office_product_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required field

  • _time
  • ImageLoaded
  • process_name
  • OriginalFileName
  • process_id
  • dest

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.

Known False Positives

Limited false positives will be present, however, tune as necessary.

Associated Analytic story

RBA

Risk Score Impact Confidence Message
80.0 80 100 An instance of $process_name$ was identified on endpoint $dest$ loading mshtml.dll.

Reference

Test Dataset

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

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