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Description

The following analytic identifies behavior related to CVE-2021-40444. Whereas the malicious document will load ActiveX and download the remote payload (.inf, .cab). During triage, review parallel processes and further activity on endpoint to identify additional patterns. Retrieve the file modifications and analyze further.

  • Type: TTP
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Endpoint
  • Last Updated: 2021-09-10
  • Author: Michael Haag, Splunk
  • ID: f48cd1d4-125a-11ec-a447-acde48001122

ATT&CK

ID Technique Tactic
T1566 Phishing Initial Access
T1566.001 Spearphishing Attachment Initial Access

| tstats `security_content_summariesonly` count FROM datamodel=Endpoint.Processes where Processes.process_name IN ("winword.exe","excel.exe","powerpnt.exe","mspub.exe","visio.exe","wordpad.exe","wordview.exe") by _time span=1h Processes.process_id Processes.process_name Processes.process Processes.dest 
| `drop_dm_object_name(Processes)` 
| join process_guid, _time [
| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime FROM datamodel=Endpoint.Filesystem where Filesystem.file_name IN ("*.inf","*.cab") by _time span=1h Filesystem.dest Filesystem.file_create_time Filesystem.file_name Filesystem.file_path 
| `drop_dm_object_name(Filesystem)` 
| fields _time dest file_create_time file_name file_path process_name process_path process] 
| dedup file_create_time 
| table dest, process_name, process, file_create_time, file_name, file_path 
| `office_product_writing_cab_or_inf_filter`

Associated Analytic Story

How To Implement

To successfully implement this search you need to be ingesting information on process that include the name of the process responsible for the changes from your endpoints into the Endpoint datamodel in the Processes node and Filesystem node.

Required field

  • _time
  • dest
  • process_name
  • process
  • file_create_time
  • file_name
  • file_path

Kill Chain Phase

  • Exploitation

Known False Positives

The query is structured in a way that action (read, create) is not defined. Review the results of this query, filter, and tune as necessary. It may be necessary to generate this query specific to your endpoint product.

RBA

Risk Score Impact Confidence Message
80.0 80 100 An instance of $process_name$ was identified on $dest$ writing an inf or cab file to this. This is not typical of $process_name$.

CVE

ID Summary CVSS
CVE-2021-40444 Microsoft MSHTML Remote Code Execution Vulnerability 6.8

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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